Comment 2 for bug 493322

If you put 800x800 as the desired size, the longest side will be 800, and the other side will be calculated to keep the same ratio. That's how I always resized my photos to publish online : I put 2000 in both field, and there you go !
So to me, the only additional option that could be added would be a tickbox called "keep aspect ratio". Because right now, if you really want 2000x2000, with a non square initial image, you cannot do it.