This isn't really a new plugin, just modified version from old OptiPNG file type plugin.
Switching old OptiPNG plugin is recommended because it uses outdated version of OptiPNG which contains security vulnerabilities.
Functionality is same and source based on I Like Pi's code, so most of the credit doesn't belong to me.
Download Plugin: OptiPNG plugin.ZIP
Download Source: http://mir.cr/3EWYQMQS
Both the OptiPngFileType.dll and optipng.exe need to be in the FileTypes directory.
October 7, 2011 - updated OptiPNG to 0.65, little reformatting to code and few changes to UI
June 12, 2012 - updated OptiPNG to 0.7.1, and tiny changes to code
I don't really care how do you use modifications I made, but because original plugin is licensed under GPLv3 this plugin is also licensed under GNU General Public License (GPL) v3