Off topic: Btw, how do you make your profile pic move?
If you ask that question, you probably wont be able to make an Add-On of any kind.
How?
just an image packaged
2Xie:2x2, 4x4, 8x8, 16x16, 64x64i think those are valid sizes
http://wiki.returntoblockland.com/index.php?title=Creating_and_Packaging_Prints/Decals
Everything you need to know:
What was the point of posting this again?