Fax For Asterisk provides the functionality to send and receive faxes to / from TDM and IP channels — TDM channels are established across Digium telephony boards and IP channels can use regular G.711 audio encoding or T.38 encapsulation.
Faxes transmitted and received by Fax For Asterisk begin and end as TIFF image files. TIFF files may be readily converted into or from other formats using standard Linux command-line utilities.
The key consideration is that unless the information that Asterisk knows about the fax is sufficiently detailed, it may not be possible to deduce the intended recipient without having someone actually read the fax (it is common for a fax to have a cover page with the recipient's information written on it, which even the most capable text recognition software would have a difficult time making sense of).
Add reliable, high capacity fax capabilities to your Asterisk system with Digium's Fax For Asterisk. It provides Asterisk dialplan functions and applications that make it easy to build custom fax solutions. It's also future-proof, offering support for traditional analog fax technologies and T.38 SIP faxing.