Comment by dkarl

Lots of image formats store arbitrary metadata (and data data) either by design or by application-specific extensions. I remember seeing seismic and medical images that contained data for display in specialized applications and writing code to figure out if binary metadata was written in big-endian or little-endian byte order (the metadata often did not have the same endianness as the image data!) For example, TIFF files containing 3d scans as a sequence of slices, with binary metadata attached to each slice. If you opened it up in your system default image viewer, you'd only see the first slice, but a specialized viewer (which I did not have) would display it as a 3d model. Luckily (IIRC) the KDE file browser let you quickly flip through all the images in a directory using the keyboard, so I was able to dump all the layers into separate files and flip through them to see the 3d image.