The exact resolution of the image itself is 1862x1591. I believe that thumbnail links to a kind of "overall view", you have to aim the picture again and click the zoom icon that appears in it's right corner (it's called "view image" which finally leads you to the image itself).
In photobucket there used to be a nice function than a thumbnail was opening an image in a new window just as a new file, with full resolution. It seems to be not working anymore, because if I edit the code of it and it works for me, after refreshing it's again forwarding to this photobucket gallery page. Can't help it.