I had so much problems with that until I realized it wasn't the picture at fault, (it kind of is if anything lol), but it was the size. I would try resizing it on a good program or a website that does good resizing?
edit: I think GIMP/Photoshop can do this, and once I went onto this website, Iaza, and I found a column that did resizing. Hoped this helped.
Or just get a new picture.