OptiPNG is a PNG optimizer that recompresses image files to a smaller
size, without losing any information. This program also converts
external formats (BMP, GIF, PNM; TIFF support is coming up) to optimized
PNG, and performs PNG integrity checks and corrections.

The idea has been inspired from pngcrush, and is explained in detail in
the PNG-Tech article "A guide to PNG optimization". The implementation
is carried forward in OptiPNG, which offers a faster execution per
trial, and a wider search space.

WWW: http://optipng.sourceforge.net/