Okay. I'll actually try to help you out here a little bit. I think what you meant to say is your profile picture, not your avatar. An avatar is the picture that shows up beside everyone's posts, and a profile picture is what you see on their profiles. If you want to upload a profile picture than click on "User CP" and then on "Edit Avatar". You then can enter a url or upload a picture directly from your computer.
If you want to upload a picture straight onto here in your posts and it won't load or just becomes a confused cross breed, then try cropping it a bit. I have to do that to all of the pictures that come off one of our cameras, but not the other.