Whats your background color? black or white i guess? You would have to remove that background color so it get transparent. If it's already transparent (the little grey/white squares on the background) you just need to save the picture in extensions that support the transparent background, like .png or .gif (i think).
If when you remove/erase the background color the background don't get transparent, you will have to make a new doccument and select: "background contents: Transparent". paste everything in the new doc and removed the current background color of the picture (also called Rendering, you have to be precise).
Im not too sure what was the problem exactly but i hope it helps ^^
I use PHOTOSHOP so those are the steps for it.