Alex, I have had problems in the past with thumbnails and resized images. The problem can appear to be intermittent or affect images that in their compressed form are smaller than images which seem to resize fine. I am on a shared hosting service that limits the amount of memory I can access. At least in the versions of MediaWiki that I am familiar with, the 'stock' code uncompressed JPGs before resizing them - this dramatically increased the image size. The solution that worked for me was to switch to ImageMagick (instructions at http://www.mediawiki.org/wiki/Manual:Installing_third-party_tools). In my case, I ended up installing ImageMagick myself, only to later find that my hosting provider already provided a useable (if not the most current) version. Regards, Norbert server on