I'm not sure how to do it for software, but for novels it should be easy to fingerprint. Every couple of pages the author writes a sentence twice in different forms. This would not take a great deal of extra effort on the part of the author. Software can then choose from the alternative variations in different patterns to produce a unique fingerprint for every copy. There would seem to be two approaches to removing the fingerprint. One would be re-writing every sentence in the novel. The other would be to collect enough copies to identify all of the sentences which have variations. Most of the mathematics of fingerprinting research is oriented around figuring out how many different points of variation there must be to be secure against a certain number of copies of the fingerprinted item being compared. Perhaps a similar approach could be applied to software, where in many cases a couple of statements could be trivially interchanged, or other kinds of simple transformations could be manually generated. Those could be marked by the programmers without too much extra work. I agree with Doug that fully automated fingerprinting schemes which post process "vanilla" documents are going to be forced to rely on security through obscurity, probably a losing battle. Also as Doug says the viability of legal sanctions against the source of fingerprinted docs is questionable. Maybe it could work if you had just a few copies out and the people who were given copies can be seriously held to non-disclosure agreements. Hal