GIMP - GIMP is a multiplatform photo manipulation tool.
BatchPhoto - BatchPhoto is a batch photo editing software for Win and Mac that can convert, resize, annotate and watermark hundreds of photos in one go. Learn more and try it for Free!
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Batch Image Converter - Convert multiple images, photos, and pictures between 30+ formats: JPG, PNG, GIF, TIFF, BMP, JP2, J2K, TGA, PSD, RAW, DDS, PNM, WMF, ICO, SGI, HDR, LBM