A Sprite generator for all the images included in a Tiki install: this could be cool to improve Performance but there a different points of view. Ex.: CSS Sprites are Stupid – Let's Use Archives Instead! (Firefox demo)
Would be prefer something which is part of the build process? (and thus only works with bundled images) or something run by each Tiki (a bit like minify)
Also, as of Tiki7, images are not systematically well compressed. A one time clean-up would be good. Also, making sprites would no doubt compress the resulting files.
https://github.com/pminnieur/sprites is mentioned