there are any number of resizing algorithms (bicubic, bilinear, nearest neighbour et al.) some of which are better than others, depending on the jpeg content. the same is true for gif resizing, but I reckon very few users are uploading gifs. however, the machine will likely use the same algorithm for all images, hence we can expect that some will be resized in a way that may degrade the image. e.g. bicubic is usually good to preserve the smooth gradients of a poser jpeg, but bilinear is often better to preserve sharp lines of a drawing. in any case, this may tend to slow things down, but I don't have any experience with a server doing resize on upload. the other detail (recompressing the jpeg on upload) will cause the dreaded "jpeg artifacts" to appear, hence I suspect y'all won't be recompressing them on upload.