[IanCal]

I've just tried compressing a 12 meg png file with pngcrush locally (generated with `convert -size 1000x2000 xc: +noise Random noise.png`, it only took a few seconds and didn't tax the processor much. Maybe pngcrush handles it better than other things but that didn't seem onerous.

[kamkha]

I would guess that the service does something more along the lines of `pngcrush -brute` which is significantly more taxing.