And, as Jacob says, those two operations are similar, but with differences.
The Picture is what one would see, if they clicked on your Profile, and that can be larger than the Avatar. The Avatar is what one sees, besides one of your posts, or replies. Its limits are a bit smaller. The Picture and the Avatar can be the same (within the size limits), or different.
Also note that it can take a few days, to have either/both the Picture and/or Avatar approved. I think that for my first Avatar, it took almost 8 days, and it was only two glasses of red wine.