NConvert is batch software for converting graphics files. From the author of the popular XnView.

It will allow you to import about 400 graphic file formats and export about 40 graphic file formats. NConvert supports multipage TIFF, animated GIF, and animated ICO. And you have full control over resizing, brightness/contrast adjustments, color number modifications, the application of filters (blur, average, emboss, etc.) and effects (lens, wave, etc.).