Did you consider using the new GAE API for image serving? I think it requires objects to be actual blobstore objects rather than in the datastore as a blob prop

Did you consider using the new GAE API for image serving? I think it requires objects to be actual blobstore objects rather than in the datastore as a blob property, but it does dynamic image thumbnails. It does do dynamic resizing of picture to a bunch of different sizes, but requires a slightly different workflow to get pictures into the db.