Meme: Demonstrating Collision with Photos.
Originator: Thomas Pornin.
Background: Modern cryptographic hash functions are designed securely such that it's practically impossible to find two different messages that hashes to the same value. Of course, the design of secure hash functions didn't occur overnight, and some past hash algorithms such as MD5 had been broken. In an attempt to explain the improbableness of SHA256 collision, Thomas Pornin brought up statistics showing, it's more likely to get assaulted by escaped zoo animal, than having a SHA256 hash collision and illustrated his answer with an image macro.
One month later, some unknown user by the name of Adban asked Are there two known strings which have the same MD5 hash value?, where he received an illustrated answer five years later from Silverfox, who had shown two pictures supposedly having same MD5 digest (it got altered by imgur somehow). Two pictures, one showing a shipwreck, the other an fighter jet crash, invited a pundit commenting:
... Btw only looking at the pictures clearly shows there is a collision somewhere… ;-)
Also: Not related, but Google together with researchers in Netherlands demonstrated world's first SHA1 collision with two PDF files.