Opal has extensive support for fax. This operates on both SIP, H.323 and even PSTN. It relies on the external package spandsp.
Building from source
For Linux, spandsp is usually available as a development library in most distributions. If installed configure will find it and it will be included.
For Windows you will need to download the |tarball]] and build it.
After installing SpanDSP, simply then use the spandsp_fax_2005.sln or spandsp_fax_2008.sln file to build the plug in. Note Visual Studio 2003 is not supported.
Note, this will automatically try and download libtiff, another open source library for TIFF file operations. Thus the first time you build it you should be connected to the Internet so the download can proceed.
Then copy the following two files from:
to C:\PTLib_Plugins, or wherever you have set the PTPLUGINDIR environment variable. It should work in the same directory as your application as well.
Additional note: If you get errors building libtiff, you may need to edit tiff-3.8.2\libtiff\tiffconf.h and comment out the entries for JPEG_SUPPORT, LZW_SUPPORT, PIXARLOG_SUPPORT and ZIP_SUPPORT.