I have scanned some photos of mine from prints, and I would like to mark them with some indication that I took them. Is there a recognised way of tagging photos that might survive some basic post processing?
I don't need it to be secure, just for the data to be kept if the photos are copied, maybe cropped or touched up a little.
If you can import the scanned photo into any kind of photo-workflow software, such as Lightroom, then you can add information into the "Author" and "Copyright" fields of the EXIF data. Then, when you export the file, this will be baked in to the JPG.
Alternatively you could add a watermark to the photo, though personally I hate these as they detract from the photo itself.
You can do invisible digital watermarking that can survive quite a lot. There is a quick-and-easy commercial solution, Digimark, that's been built into the menu system of most of the image editors I've used over the last decade or so (all of them commercial products -- I haven't met a FOSS UI that I've been able to come to terms with yet). You'll be prompted to get an ID on your first use.
There are probably other, similar utilities available, and it's easy enough to home-grow a solution using the image math option and noisy, low-contrast text on a mid-grey background, but they don't have the benefit of making the sirens and whistles go off at a commercial print shop. There's not a lot you can do about digital reuse except to prove that the image is yours if you find somebody using your image.
If you're a professional and you're serious about protecting your images, you probably need to use invisible watermarking as Mr. Rogers said. As Mr. Rogers implied, a Digimark subscription would probably be ideal. It is way too easy for someone to alter the Author and Copyright metadata that Mike described. Digimark is the only method I am aware of that will provide you with any reasonable level of protection.
