This one is easy cause it has happened to me before.
The "file size" of the photo/picture that you are trying to upload exceeds the maximum size of the photo allowed.
If u try to upload a different photo and it's allowed, the photo will appear. If the photo doesn't appear and you get a small empty small square, then the photo is simply too large on size wise. One of the mods will know the exact file size but on threads it is 2048kb. It may be the same for uploading your profile picture.
Change to a different photo and one will load if the size is allowable ! This shld fix your problem.
