Every now and then an image appears online which has people heartily debating its authenticity, arguing about its colour or asking how it came about in the first place.

There are also some amazing pictures that look like one thing but turn out to be something quite different.

We've gathered together a collection of the best from around the internet - pictures that'll have you scratching your head, questioning your eyesight and generally feeling perplexed by their existence.

Different coloured creatures

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NovickProf

Over on Twitter, David Novick, Professor of Engineering Education and Leadership, at the University of Texas at El Paso has been sharing a number of interesting optical illusions.

Including this one that seemingly shows green cats and pink dogs, yet in reality, both animals are the same colour. It's the horizontal lines that are tricking your eye. If you zoom in closely and look at a small part of each animal you'll see they are the same colour.

Floating roof

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superslomotion

We're not sure what's going on here, but it looks like the roof of this truck is floating above the ground and casting a shadow on the stones below as well. How?

This only looks normal upside down

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Period-Y

This photo of Elon Musk seems normal enough, apart from being the wrong way up. The thing is if you try to look at it the right way around you'll soon find it's not right at all.

An expanding dark mist

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AkiyoshiKitaoka

Self-proclaimed experimental psychologist Akiyoshi Kitaoka studies optical illusions and posts the most interesting ones over on Twitter.

Those illusions include the likes of this one which seems to show an expanding black mist emanating from the middle.

The four-eyed man

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Skarmavbild

This illusion really messes with our eyes and his too apparently.

As far as optical illusions go, this one is both simple and painful. Who thought two pairs of eyes and two mouths would be enough to break your brain and make it painful to focus?

Reflections on the water

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Baker359

Less of an optical illusion and more of a brilliant bit of artwork. This is a mural that was painted on the side of a building, but intentionally painted the wrong way up so it reflected the correct way on the waters nearby.

Floating speaker

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Buzzfeed

This photograph taken on the beach seems to show the speaker on a floating platform. No doubt down to our brain interpreting the shadow of the flag blowing in the wind as the shadow of the speaker's platform and microphone instead.

Another classic illusion caused by our brains trying to decipher the scene before us.

Duck or Rabbit

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Imgur

This optical illusion has taken on many different forms since it first found its way into publication in the book "Philosophical investigations" by Ludwig Wittgenstein in 1953.

Here it is suggested that there are ambiguous images that can be seen in two (or more) different ways.

In this instance, the drawing could be a rabbit or a duck or both and what you see first will be down to your perception of the world or based solely on suggestion - the duck and rabbit axis in this version make it easier to quickly decipher both variations.

Ambiguous cylinder illusion

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Kokichi Sugihara

One of the finalists for the "Best Illusion of the Year Contest" makes for pretty mind-bending viewing.

Here Kokichi Sugihara places a set of cylinders in front of a mirror. The reflection shows a different shape until the object is revolved and then we see the opposite. It's best viewed in this video.

If you're left scratching your head after watching that video, you can see a breakdown of how it works here.

Wonderfully weird greyscale store

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The Scottish Sisters/YouTube

While out shopping, YouTuber Holly McKee discovered a real-life optical illusion. Nestled away in the children's clothing section she discovered an aisle of black and white clothes that made the photo look like a filter had been applied.

When people on Twitter doubted the image wasn't edited, she took to YouTube to prove them wrong.

The Black and Blue/White and Gold Dress

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Wired

Back in the hazy days of 2015, a certain dress took the internet by storm and had everyone debating about whether it was white and gold or black and blue.

The simple garment was the perfect example of an optical illusion that was no illusion at all. It was, in fact, just a scientific demonstration of how the eye sees things differently in varying light sources and how our brains all handle this interpretation in ways that are unique to us.

The non-red strawberries

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Motherboard

Like the white and gold/black and blue dress, these strawberries are an optical illusion caused by something known as colour constancy, which is a feature of the way we perceive colours under varying light conditions.

There is no red in the picture and yet our brains clearly interpret the red of the strawberries as still being there – assuming you're seeing them under a blue light source and extrapolating accordingly.

Anamorphic graffiti

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Sergio Odeith

Incredible street artist Sergio Odeith turns everyday corners in the real world into incredible three-dimensional artworks with ultra-realistic anamorphic graffiti painted across different surfaces to give the illusion of a depth that doesn't exist.

Letters leaping out of walls, creatures lurking in corners, other worlds coming to life in the corner of a forgotten space. His works play havoc with the eye and create marvellous murals that are a pleasure to behold.

The Bridge to Nowhere

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Martin Ystenes

The Storseisundet bridge is one of the largest bridges in Norway and photographed from the right angle it gives the impression of being a bit of road that comes to an abrupt and dangerous end some 75 feet above the ground.

However, the bridge is actually a cantilever design with a curve to it that simply makes it arc away into the distance.

Anamorphic advertising artwork

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Ray Bans

In 2013, eyewear manufacturer Ray-Ban teamed up with optical illusion masters Brusspup to create an ad campaign which included anamorphic illustrations which look like real three-dimensional objects from the right angle.

The globe and baseball are the standout pieces of this artwork and we think they're thoroughly impressive. For more optical illusion goodness, check out Brusspup's Youtube channel.

Neck or back?

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@LilMaarty

Is this a woman's back or her head and neck? The internet couldn't decide, can you?

In 2018, Twitter user @LilMaarty posted this image, apparently confused over whether the photo showed a woman's back or just her neck. The Tweet was the subject of much debate and was retweeted over 30,000 times. It turns out it is her back, in case you're wondering.

The shoe

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Nicole Coulthard

First, we had the dress, then we had the shoe. In 2017, an innocuous photo of a trainer was posted online in a Facebook group. The poster wanted to know what colours people saw - pale pink and white or blue and grey. It was a subject of much debate and had Twitter all in a flap too. It was eventually revealed that the trainer is, in fact, pink and white, if you saw anything else it was a mere trick of the light or down to how your eyes perceive colours.

The Infinite Chocolate Bar

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Pigeon Toes

Can you make a never-ending chocolate bar by simply cutting it and repositioning the chunks? No. But it makes for an interesting illusion.

This tasty illusion apparently shows a way to get never-ending blocks of chocolate out of a single bar. Alas, it's all a trick and simply involves a shorter and shorter bar. Still pretty clever stuff!

Confusing shadows

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Mouse_fighter/Imgur

Another brilliant optical illusion created simply by the sun being at a specific place in the sky. This one seems to show oddities in the windows caused by their shadows which makes the building look like it belongs in Inception.

Wooden Train Track

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Youtube

In another Tweet-storm, yet another optical illusion based on an everyday object appears to confound logic and physics. One wooden train track block is apparently longer than the other, yet when put on top of the other, they're the same length. How?

The solution to this apparent mystery is contained within the replies to the initial Tweet, but we'll let you enjoy it in the meantime.

The Negative Lady

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Metro

This illusion requires you to stare at the white dot on the woman's nose on the left for 15 seconds, then look to the right of the image at the blank space. You should see a flicker of the full-colour photo of the woman.

This is down to the way our brains interpret imagery and colours and in this case is known as "negative afterimage", which was explained by Dr Juno Kim from the University of NSW School of Optometry and Vision Science to Daily Mail Australia:

"The code for all the hues we can experience in the light spectrum – this information is relayed from the back of the eye to the brain via three opponent neuron channels.

"When you look at something that, for example, is yellow for a long period of time, you stimulate the cells that are positively sensitive to yellow – so in the yellow and blue channel.

"The cells’ activity increases and after a bit of time the activity fatigues and declines.

"When you then direct your gaze at a uniform background – let’s say a grey wall – then what happens is that the cell doesn’t return to its resting activity, it goes much lower than that.

"It’s that decline – the weakening of the yellow code – that codes for the opposite colour to become stronger, so you’ll see blue."

The awkward dots

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@wkerslake

A simply brilliant image that plays real havoc with both your eyesight and your brain. This image was shared by Will Kerslake on Twitter with the caption "There are twelve black dots at the intersections in this image. Your brain won’t let you see them all at once."

We have managed to see them all, but it's not easy.

Shiny legs or paint

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kingkayden

This is an unusual illusion, at first glance you'll probably spy a pair legs that seem to be covered in oil, but given a second to look again and you'll see they're actually spattered with white paint.

Video game or real life?

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mike_pants/Reddit

This image was taken in Hawaii and shows a weird time of day when the sun is at such a perfect position in the sky that no shadows appear near these posts. The result is what looks like video game rendering rather than real life. You have to look a few times to establish a firm sense of reality with this one.

iPad Car Seat

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9gag

Sometimes an illusion can be as simple as a pattern blended into another in the same way that camouflage works.

This photo was posted on 9gag with the headline "Just spent 30 mins searching for my Dad's iPad" – can you spot the hidden tablet in the photo?

Underwater Girl

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Imgur

This photo appeared on Imgur and caused a bit of a splash. A little girl appears to be jumping into a swimming pool while simultaneously blowing bubbles like she's already underneath the surface.

Commenters quickly pointed out that her hair is dry and the apparent air bubbles could just be droplets of water from the splashing, but no conclusion was reached as to what was actually happening.

So many questions.

Log or dog?

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esquonk/Reddit

A simply perfectly timed photo of a pooch having a rest near a felled log. The result is a mild optical illusion which makes it look like the dog has either been sawed in half or is a break in the make-up of reality. Barking mad.

The revolving snakes

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Google+

This one is a simple trick of the eye. This is not an animated picture, it's a static file that shows a mass of intertwined snakes. But if you stare at different sections you'll see the snakes writhing and squirming.

The cuddle

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ibigdan

There are a few of these sorts of optical illusions on the web – a simple image of two people embracing throws your brain into confusion where the couple are at strange angles and it's hard to immediately decipher which head (or other body part) belongs to which person.

Owl Eyes in coffee

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doodlewhale

Here Stuart Rutherford managed to magic an owl's face inside his coffee mug by simply dropping a couple of Hula Hoops into the mix.

Magic Eye Shark

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Blake Lively

In the 1990s, Magic Eye was an extremely popular series of books which allowed people to see 3D images by focusing on an otherwise 2D image – usually in the form of a non-descriptive pattern.

Last year Blake Lively posted an image to her Instagram account showing a Magic Eye-like image to help promote her shark movie "The Shallows".

If you're struggling, the official Magic Eye website has instructions on how to view the 3D images but basically you're trying to focus through the image while looking at it (or blurring your vision until it becomes clear).

Common Sense Crossing

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Erik Johansson

Erik Johansson is a Swedish photographer and a whizz with Photoshop who likes to take real photographs and turn them into surreal optical illusions.

Common sense crossing is just one of his many works and one that we find particularly messes with our eyes!

Munker illusion

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@NovickProf

This is a Munker illusion, the combination of colours confusing your brain and tricking your eye to see something you know can't be right.

These tennis balls appear to be different colours - pink, green, white and yellow. They're actually all the same colour, but the addition of the coloured dots confuses your brain into seeing other colours.

Shadow man

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@interest_mild

A simple photo of a mountainside that shows a man's head apparently cast across the snow. A shadow creating a brilliant illusion that we love.

Pigeons looking for their car

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TastyTalk/Reddit

Sometimes optical illusions are just the result of an interesting perspective. This image was taken showing two pigeons perching on the edge of a ledge of a building, but it ends up looking like two massive birds looking to see where they parked their car

Glasses that have eyes

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2mamas/Reddit

This simple illusion is created by having a reflection of a nearby lamp showing in the lenses of a pair of spectacles. The resulting photo seems to show eyeballs staring back at the viewer from the glass.

The broken bike

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Remin/Imgur

This image of a bike sitting with its wheel in a puddle really wreaks havoc on the brain. The reflection appears to show a perfectly formed wheel, while the actual wheel seems bent and contorted in unpleasant ways. Which is the reality?

Floating ships

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bart59/Reddit

You would be forgiven for thinking this image is just a really bad Photoshopping, but it isn't. As one Redditor suggested, it's likely the result of a Fata Morgana mirage.

A visual illusion caused by rays of light being bent as they pass through different temperature plains. The difference in air temperature acts as a lens - refracting light and distorting images as we see them.

Hyper realistic drawings

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Howard Lee

Magnificent artist Howard Lee creates hyper-realistic drawings that are so brilliant it's hard to tell them from the real thing.

This talent for creating optical illusions is demonstrated in his Youtube video which shows him cutting, bashing and setting fire to the real versions of his creations.

Papa John's Pizza man

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Papa John's

Every now and then advertising companies do something clever that captures our imagination. Something as simple an optical illusion can be enough to help a brand stick in our minds.

This advert from Papa John's pizza was deemed clever enough to win an award at the Cannes International Advertising Awards and simply featured a mini pizza delivery man on a bit of card that could be put on someone's front door so when they looked through the viewing hole they saw the man on the other side.

Making the impossible seem plausible

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Honda

In another advertising campaign, Honda produced a video featuring a range of optical illusions to help sell their new CR-V – all aimed at helping to promote a big car experience but with a smaller economy vehicle.

3D drawings

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Stefan Pabst/Designstack

Stefan Pabst is yet another talented artist with the ability to create optical illusions from drawings, paintings and sketches. In a series of works he creates the illusion of three-dimensional images on flat paper surfaces.

Warning, contains spiders.

The spinning spiral

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IMGUR/imttoodattoo

Another classic deception. This image is not animated, it's just a simple JPG, but if you're reading this text then you're probably seeing it spin out of the periphery of your vision.

The flying weightlifter

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allthingsgym

Lesman Paredes was pretty happy with his performance at the Junior Weightlifting Championships in 2015 so much so that after completing a 230kg clean and jerk he can be seen taking off from the ground.

Alas, this is not the case of Superman finally revealing himself to the world, but simply a combination of bouncy surface underfoot, heavy weights being dropped after a successful lift and a well-timed super celebratory jump. Unsurprisingly, the photo was later subjected to a Reddit photoshop battle.

You can see it all in action in this video.

Black and white photo

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Øyvind Kolås/Manuel Schmalsteig

This is a black-and-white image with the addition of some coloured lines on it. Your brain interprets those lines to see a different reality.

Shoulder rubs

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Troxicity

Sometimes it's simply timing, angle and pose that create an optical illusion. Here this sailor appears to be getting a shoulder run from the sun that's behind him simply because it lines up nicely with his epaulettes.

Pixelated leaves

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Kraynix

This leaf looks like it belongs in Minecraft rather than the real world. Yet here is, existing with its odd-looking multi-coloured finish.

Wall mounted

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Sobek188

This one looks like one of those photos of bogus bodge jobs that cowboy builders have made. A TV screen seems to be embedded in a wall. Very odd.

Weird lines

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jatadharius

At first glance, there's nothing off with this photo. But then when you spy the construction of the pillars and the straight lines through the middle your eyes might struggle to take in the view.

What's going on with the floor?

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starlinguk

This massive ancient building sure is impressive, but what is happening with the floor? It's really playing havoc with our eyes.

Half empty or half missing?

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JelaniKazu

This chap sat down at school with a drink cup that looks especially weird on the desk. Where's the rest of it?

Well, there's a hole in the desk and the fluid inside is just the right height to block the rim, resulting in a curious optical illusion.

Paper thin building

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JelaniKazu

It seems that from certain angles some buildings look like they are made of nothing and are defying all laws of gravity and psychics.

Invisible car

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Reddit

This automotive mishap has left a car's front bumper behind. But somehow it looks like the car is mostly invisible or somehow breaking through from another dimension.

Pixelated dog

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ClassicDimension

Another photo that looks like something that belongs in Minecraft instead of the real world. Just a dog peering through a window.

A chandelier in the sky?

Optical illusions photo 1
exemplariasuntomni

Is that a chandelier in the sky or a particularly interesting UFO-like none you've ever seen (or not seen) before?

No, it's just an optical illusion likely caused by reflections but a cool one nonetheless.

Time falling away

Optical illusions photo 2
mark_peters

This one looks like something has gone wrong with time. The hours and minutes are just slipping away.

But no, it's just a broken watch.

The house is on fire?

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PeteLX

Sometimes optical illusions just happen naturally. Here, a sunset has reflected on the window of a building in such a way that it looks like the residence is on fire.

A moving circle

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AkiyoshiKitaoka

Another of Akiyoshi Kitaoka's interesting images, this one appears to show a circle in the middle the picture that moves. Scroll up and down past it and you'll see it shake. The same effect can be achieved by simply moving your eyes around the image.

Accidental giant

The subject of this photo is apparently a bit of a giant in real life, towering at around seven feet, but here with the help of some interesting perspective he appears to be an actual giant, with tiny onlookers in the background.

An ancient optical illusion

elephants optical illusion

This might be one of the oldest optical illusions on our list. It was apparently crafted by the Chola dynasty in India and may be as much as 900 years old. It shows two different animals seemingly entwined with one another, yet if you look carefully you can see each of them. The outlines in this image certainly help.

There are no curved lines

This is an odd one. When you look at this image you'll see plenty of straight lines along with some curved ones. But when you move your eyes around the image to look at it you'll notice the curves disappear but reappear elsewhere. Essentially there are no curved lines, it's just an illusion.

Not a crow

not a crow
@RobertMaguire_

Sometimes an optical illusion can just be as simple as a photo taken at the right angle with a weird bit of perspective. Like this photo of a crow that isn't a crow at all.

A scrolling illusion

Some of these illusions only become illusions when you interact with them in some way. For example, with this one, you'll see an arrow appear when you scroll up and down the page while it's in view.

Not a caterpillar

Another instance of an illusion simply being created by your brain not understanding a photo. This image initially looks like a furry colourful caterpillar but is actually just a bunch of birds on a tree branch.