Usingmac.com had a useful tip: How to resize multiple images using Preview. I tried it, it does work on Leopard. This seems like a great way to create a bunch of thumbnails. Be careful, though, when you save the resized images. It overwrites them. I copied the images I wanted to resize to a new folder, then resized them. Keeps my original images as is.
- Open images to be resized in Preview
- Select images you want to resize.
- On the Preview menu Tools -> Adjust size.
- File -> Save All The images are overwritten.