BIMP- Batch IMage Processor. A batch image editor which allows you to perform various functions on multiple images.
BIMP is a must have utility for webmasters (thumbnailing etc.) and people with digital cameras, and best of all it's absolutely FREE!
Functions: Resize, Prefix Filename, Suffix Filename, Remove Spaces, Antialias, Emboss, Rotate, Flip Horizontally, Flip Vertically and Change Format (i.e. BMP, JPG, GIF etc.).