The following are a set of related works surrounding the development of methods to embed visual information which are unobtrusive to the human eye but meaningful to the cameras. If you know of interesting work, please e-mail email@example.com to be included here. Or, if you have time to help turn this into a wiki, do it. I will link directly to your wiki.
If you are wondering why wikipedia is being used here, it's because it's readable by non-experts, comprehensive and collaborative with your participation. You may even consider donating.