Zero-Width Characters: Invisibly fingerprinting text
This is a pretty common method of watermarking sensitive content in EVE Online alliances, however we've found it suffers from some serious drawbacks.<p>Zero-Width characters tend to cause lots of issues when they are copied and pasted, which may alert a poorly equipped adversary that they're handling watermarked content. In addition, entities that are aware that you're watermarking text content in this way can just take screenshots of the text, transcribe it, or strip it of all non-ASCII characters.<p>The best solution I've seen is something I like to call "content transposition". The idea is that you take a paragraph of content and run it through a program that will reorder parts of content and inject/manipulate indefinite articles in order to create your watermark, while keeping the content grammatically correct. That way even if an adversary is fully aware that you're watermarking text content, they need two copies of the watermarked text in order to identify and strip your watermark.