OptiPNG is a PNG compression optimizer.

In the typical use case, OptiPNG recompresses PNG image files
losslessly, converts external formats (BMP, GIF, PNM and TIFF) to
optimized PNG, and performs PNG integrity checks and corrections.
At the user's explicit request, OptiPNG is also capable to alter
image data or remove metadata.

OptiPNG is open-source software, distributed under the zlib license.
For copyright and licensing terms, see doc/AUTHORS and doc/LICENSE.