1) The avatar you made for Krackshot is too big. It shouldn't be bigger than 100x100 pixels.
2) If you can, please save your work in .png format. The quality of the picture is that much better than .jpeg's
Usually, Numot, things like that are caused by quality settings when you go to save your file. Check all the "options" on whatever program you are using, and make sure all the possible quality settings are set at 100%, and you have it set up for the biggest file size possible (and hence, max quality). It really looks like you're saving JPGs at 85% quality (which I think is the default in Gimp, I'm not sure) and 2x2x1x1 for the colors (when the max for color definition in Gimp is 1x1x1x1, which is about 60% bigger in filesize or something).