I use imagemagick, using this commandline (both for the image and the thumbnail): convert -filter ***** -resize x! -quality ** image.bmp lowresimage.jpg filter=lanczos for more detail, triangle for less detail (more compression). resize=size of new image quality=usually 90 or more. If i have large tumbh i use sometimes 89, which is very smaller in size than 90. It's a very nice program..... i use it also to put border and title on my prints.....