ImageMagick 7
A modern, cross-platform, 2D Graphics library for .NET
PHP Image Processing
A powerful, free and open-source tool for TextureAtlases/Spritesheets
High performance Node.js image processing module
Resilient Image Library - successor to DevIL
Java Image Processing Program
BRIC is a powerful tool for batch image processing.
Add watermark to any image or photo (batch processing available).
View and alter images (batch processing available).
iwatermark is a image watermarking web application.