Well there's tons of software that can be used, although a 30 day trial program could be a bit OTT if you need to convert a pic every now and then .. annoying when it runs out anyway.
Freeware image converty software is probably the best way to go..
You're right, of course. The major programs are just the easiest ones to find and install quickly. If you're as lazy as me, then you don't want to spend ages searching through freeware download pages...
Anyway, I forgot about The Gimp, which is free, and rather nice. Everyone should have a nice paint program anyway