I use G.I.M.P. its basically a free photoshop and i am glad you like it
oh and i will tell you how to use spoilers,
Click on "quick links" then "edit signature" then put in,
[spoiler*][img*]http://projectpokemon.org/forums/picture.php?albumid=25&pictureid=421[/img*][/spoiler*]
Without the * and it will look like this,