OK, so Imagemagick seems to be the tool of choice. How do I decide what size to make the JPGs? I don't want to have to individually decide for each picture, most will start as 3264x2448 but I can't guarantee that they're all that size. So, say I decided that a maximum dimension of 1024 pixels made sense how do I automate converting a random collection of JPG images to <=1024 in either direction?
So, the -resize option actually defines a bounding box.
I.e. if you use:
convert in.jpg -resize 1024x1024 out.jpg
out.jpg will be an image that will be at most 1024x1024, but could be 768x1024 or 1024x768.
If you wanted to make sure that you only resize things that are already bigger than 1024x1024, you'd do:
convert in.jpg -resize 1024x1024> out.jpg
Thanks,