Having successfully sorted out a previous thumbnail issue (thank you all for that), I have a new problem.
As opposed to sticking with the thumbnails created by default, I've uploaded my own that are cropped to the size I'd like. However, the automated greyscale image is still being resized, and so is smaller than the initial thumb!
Check out a screenshot here: http://twitpic.com/9kz0cx
Any help is greatly appreciated