Is this the message you're getting? (It may say something other than "gif".)
Can we assume you are trying to load them from your PC using the AAPK "Upload Attachment" feature and not directly from your phone?
I doubt it's the size. I've seen people post 15 megapixel pictures on here (TURN DOWN THE RESOLUTION ON YOUR CAMERA
). It's almost always the file extension if you're trying to load them through AAPK. Pictures stored on a web site such as but not limited to Photo Bucket are not limited to .jpg file extensions.
I tried to find the file format in which the Motorola Droid stores pictures and all I could find was the file formats the phone supports. Sooo it could be storing them in a format other than .jpg (same as .jpeg).
Image file format supported:
Edit: Motorola tells me the file format the Droid uses when it stores the pictures is .jpg and you can't change it to any of the other supported formats.