snowdrop

Snowdrop provides reliable, difficult to remove steganographic watermarking of text documents (internal memos, draft research papers, advisories and other writing) and C sources (limited distribution software, licensed software, or freely available code) so that: (1) leaks can be identified if the data goes public. (2) original source can be determined and demonstrated if part of the document is claimed by somebody else, copied without permission, etc. Snowdrop uses redundant steganography using four different logical channels, and should be proof to many modifications, including reformatting, spell checking and so on.

Only use this tool against systems you own or are explicitly authorized to test — see the disclaimer.