Import from computer help?

I'm new, so I'm having troubles. The main thing is, I like to hand draw first, and then fix it up and color it using the computer. I scan in the pic i've been working on, but when I try to import it from my computer, It wont accept it, and I can't figure out why.
If it's any help, i save my photos to Jpeg and I'm using a mac. I know alot of things don't like macs. Any help would be appreciated. Smile