Converseen
http://converseen.sourceforge.net/

If you are looking for a way to convert, resize, rotate and flip an unlimited number of images, Converseen is worth a look. It’s an open source program that supports over 100 image formats and the user interface is easy to use. The site for the program includes a FAQ area and this version is compatible with Windows and Linux operating systems. This will be added to the tools section of Research Resources Subject Tracer™ Information Blog. [From The Scout Report, Copyright Internet Scout 1994-2013. https://www.scout.wisc.edu/]