>>3698
Gotta look up PNG format specifications. PNG uses DEFLATE, which is a Hoffman compression algorithm for the actual pixel data, so you'll need to look up how those work. Because of the compression, adjusting one byte can make huge and unpredictable changes.
JPEG is what most people hack. It stores 3 different monochrome images for red, blue, and green. That gives it the stripes of discoloration when it's hacked.