From JG Mini-Tools:
The Mass Image Resizer is what you might call a mini-app. It is a focused application built to solve a common problem of resizing and resampling a large number of images. The purpose of the application is to save you time in resizing a large number of images (you may also change their DPI). Version 1.0.1 added the capability to convert images from one file type to another (e.g. .jpg to .gif).