We all keep in mind the “What color is this dress?” phenomenon adopted by “Yanny vs. Laurel.” Now the world has a brand new puzzle to obsess over, and it’ll pit Apple customers in opposition to their longtime rivals.

Here’s the way it works: have a look at the beneath picture on a PC or Android cellphone (or some other non-Apple product). Then, view the identical picture on an Apple gadget. If you had been already utilizing a Mac, iPhone, or iPad, then swap over to a distinct platform.

Let’s attempt that once more with a distinct picture.

Pretty neat, huh? When viewing the primary picture on a PC or Android cellphone, it is best to have seen the message “HELLO WORLD.” On an Apple gadget that very same picture file reads “HELLO APPLE.” (There is a caveat that we’ll deal with in additional element beneath.)

The second picture is even trippier. On a non-Apple gadget, the picture reveals an outdated IBM PC, however swap to an i-device and also you’ll see an outdated Mac.

OK, so what the hell is happening right here? Let engineer and cryptographer David Buchanan—the mastermind behind this puzzle—do the explaining:

“I found this while writing my own multi-threaded PNG decoder. While pondering my design, I realised that I had an exploitable implementation bug,” Buchanan wrote in a blog post. “After learning that Apple has their own implementation of parallel-decodable PNGs, I realised that they’d made exactly the same mistake!”

In simplified phrases, there are alternative ways to decode a picture. You may do it in a single thread or you may do it in parallel threads damaged into blocks (a way used to make packages run quicker), as Buchanan tried. He found a bug in his personal venture, then discovered that Apple had made the identical mistake. He decided that it was potential to render a PNG file the place: decompress(a + b) != decompress(a) + decompress(b) (the place != means not equal to). That is, that two components decoded individually then put collectively didn’t all the time create the identical outcomes as those self same two components decoded collectively.

“This could happen if a ends midway through a non-compressed block. It is, therefore, possible for an image to have two possible interpretations, depending on whether a parallel or non-parallel decoder decodes it,” Buchanan continued.

For you skeptics on the market, once I confirmed these pictures to my brother, a analysis scientist at The University of Virginia, he hashed the recordsdata (transformed them into numbers) and confirmed that they’re certainly the identical, proving that Buchanan isn’t slicing corners by serving you completely different recordsdata primarily based on the browser or OS you’re utilizing.

If you’re having hassle replicating this puzzle, it might need to do together with your browser as a result of the trick depends on Apple software program, not {hardware}. After viewing the picture on a number of gadgets and browsers, we realized that Apple merchandise operating Safari will all the time present HELLO APPLE whereas non-Apple gadgets utilizing different browsers present HELLO WORLD.

But issues do get complicated when you begin mixing and matching.

When utilizing non-Safari browsers on Apple’s cellular gadgets (iPad, iPhone), the HELLO APPLE message appeared. Strangely, utilizing those self same browsers—Chrome, Opera, Edge, for instance—on a Mac confirmed the HELLO WORLD message. While we will’t be sure, this means browser apps written for the App Store are utilizing Apple’s PNG rendering picture library whereas browsers downloaded as packages on macOS use their very own PNG parser.

Whatever the case, if you wish to get in on the enjoyable, Buchanan posted a software known as ‘Ambiguous PNG Packer’ that lets anybody create pictures that look completely different when run by means of Apple software program. We ought to warning, nonetheless, that these deviations in parsing picture recordsdata may very well be a safety concern, and one thing Buchanan believes “needs to be approached with care.”