It looks a little bit off to me. Maybe you saved it in other format than .bmp and then you changed it; I don't know. But if this image was .bmp or .gif from the start, it would look different. OR you forgot to index the picture, OR it's because of the site you uploaded it (it happened to me a few times).
Anyways... It doesn't matter that much unless you plan to make a wip out of that sprite.