Is it only that one picture of Zam that is causing the problem? If you haven't had the problem with any other pictures I'd start to suspect the image is slightly corrupt somehow. Maybe open it in some editor or other and save it as another format or edit a single pixel or something to get it make a fresh file.
I’ve tried other pictures and other files, but so far they have all been of Zam. I was really surprised when the Jenna picture worked fine, but Zam didn’t.
Oh, and I did take that image and make modifications to it to shrink it down to the official 263x320 size that OggDude had mentioned, and manually added some pixels along the left and right-hand sides to make it fit the slightly changed picture ratio.
And yet, I still had exactly the same problem.
So, we know that generating a new JPEG from the old one doesn’t help. And I don’t think that there are any “dangerous” artifacts that should be able to survive that kind of an external image resize operation.