Jpgtn generates smaller JPEGs from larger ones. It can work in batches and create new files with names based on the names of the source files. It can dump a single thumbnail to stdout for use with pipelines or CGI programs. Thumbnail size and quality can be controlled by switches on the command line. There is no maximum "thumbnail" size, so it can be useful for creating images suitable for web publishing from very large images such as those taken with a good digicam.
SIP provides image processing, pattern recognition, and computer vision routines for SciLab, a Matlab-like matrix-oriented programming environment. SIP is able to read/write images in almost 90 major formats, including JPEG, PNG, BMP, GIF, FITS, and TIFF. It includes routines for filtering, segmentation, edge detection, morphology, curvature, fractal dimension, distance transforms, multiscale skeletons, and more.