If you're interested in fax and software development, a really great book is The Fax Modem Sourcebook, by Andrew Margolis. I've had a copy of this for many years, and it's now back in print and on sale at Amazon.

Although some of the technology he talks about is now out-of-date, and it won't tell you about new developments like colour fax, it's a great book for understanding the operating principle of fax, and for explaining a lot of the terminology. Margolis also has a website where he publishes errata for the book and updated versions of his fax toolkit.