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Comment by egypturnash | Hacker News Reader

Similar, prior work: the video game "Spore" let you export a PNG of the creatures (and other things) you made with its many, many editors. It'd output a PNG of the critter, with all the data needed to build it from Spore's parts library encoded in the least significant bits of the pixels; you could easily share it in email/chat/whatever, then drag it into Spore to get the critter.

Lots more appealing than a square of grey noise, lots easier to understand when you run across it a year later...

edit: some more details on this, with examples https://nedbatchelder.com/blog/200806/spore_creature_creator...

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Pico8 does the same thing http://pico-8.wikia.com/wiki/P8PNGFileFormat

There is also Jmol, a molecular editor, that allows you to save scripts as .pngj files:

http://wiki.jmol.org/index.php/File_formats/Compressed

A video game I contributed to, Gang Garrison 2, stores maps as PNG files where the image is the actual level background, and other data is hidden in a text PNG chunk. Hides data in the file format, not the image proper, but a similar idea.

Someone did something similar to make a point during the 3d printed gun debate. There's a .png floating around of the PM522 (3d revolver) with the print files encoded directly in the image. IIRC it just requires zipping and changing the extension to load correctly.

That's just concatenating the files together and relying on the zip extractor to ignore the PNG part of the file, rather different than actually embedding it in the image data itself. I remember this being a popular way to upload non-image files to certain imageboard websites a few years back, to get around them only allowing image uploads. JPG+RAR was the usual choice.

The data was visible as a block of jumbled pixels as the bottom, not sure how concatenated files render visually (especially jpg format), so for all I know it may have been exactly what you're describing. Pretty sure I found it on an image board anyway.

That's how it looks when you concatenate two file types. I guess in theory if you make the image a pixel, you effectively get the same output but with way less effort.

A clever use of steganography, it seems, but one that would probably be ruined by image "optimizers" that are all too common today.

I suspect that is exactly why they encoded it into the pixel data rather than extra tEXt blocks. Extra blocks and metadata like EXIF and geotags get reaped by optimizers but pixel data is pixel data. (unless you resize or alter color depth.)

Or your favourite social media platform indiscriminately converts PNGs to JPGs.

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