I like to use mogrify, which is part of the imagemagick project, and exists on various operating systems (
http://aminet.net/search?query=imagemagick). It is a shell command that does a lot of things. Let me give you a few examples.
- batch image resize keeping ratio intact
mogrify -verbose -resize 800x800 -quality 80% *.jpg
- batch image resize to the dimension exactly, stretching the images
mogrify -verbose -resize 800x600! -quality 80% *.jpg
- batch image resize keeping ratio intact, auto rotates the images if the orientation info exists in the exif info of the file
mogrify -verbose -resize 800x800 -auto-orient -quality 80% *.jpg
- batch image like previous example, but enhances the colors and brightness of the images, for better quality
mogrify -verbose -resize 1000x1000 -auto-orient -quality 85% -normalize *.jpg