Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
Ralpha Image Resizer - High-speed image batch conversion tool
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.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
GIMP - GIMP is a multiplatform photo manipulation tool.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.