OptiPNG is a PNG optimizer that recompresses the image files to a smaller
size, without losing any information.  The idea has been inspired from
pngcrush, and is explained in detail in the PNG-Tech article:  "A Guide
to PNG optimization"
<http://www.cs.toronto.edu/~cosmin/pngtech/optipng.html>.  The
implementation is carried forward in OptiPNG, which offers a faster
execution per trial, and a wider search space.