@Alex, there are many GIMP tutorials online, and maybe this link would be a good starting point:
http://www.gimp.org/tutorials/ . (unfortunately, I never felt comfortable with the interface, so my knowledge is only incidental)
@SBT, I wanted to try your step-through, but the Internet Explorer v9, which I am locked into using, doesn't have the option to open an archive.org reader page in a new tab, the option is grayed out. It only allows Save Picture As, Email, Print, etc. What browser are you using?