The biggest reason to not use jpeg for pictures of text [1] is that as more compression is applied it discards the higher frequency components first. Text being

The biggest reason to not use jpeg for pictures of text [1] is that as more compression is applied it discards the higher frequency components first. Text being full of thin little lines (aka high frequency changes) is one of the first things to be mangled. A quick little test I ran was to take a screenshot of my desktop and the file sizes were: PNG: 735k PNG (optimized w/ pngcrush): 589k JPEG 80: 660k (minimal artifacts, but they can be seen on inspection) JPEG 30: 313k (text regions are starting to get muddy and take more effort to read) JPEG 10: 163k (this is like trying to read text in a colorblindness test, lot of distracting artifacts) On a more positive note, I enjoyed browsing your Documents folder :) [1]: IMO screenshots should use lossless formats in general