You can set characteristics by hand, of course, but Neatnik allows you to batch-process the contents of a folder (including all levels of enclosed folders) or of an entire disk.
Create an encrypted disk with software that comes on your Mac view it
Pt. 1: Finding the Finder view it
IfranView is a powerful free tool for batch converting image files. view it
Using TuneUp Utilities 2009 to clean up your drives view it
If you're having trouble with a drive you can verify and if necessary, repair it view it