I'm going to be distributing some of my images as TIFF files and want to put my copyright and contact information into the metadata for the images in a way that prevents it being stripped or altered by third parties. At the moment I'm using Photoshop CS5 and inserting the information using Bridge. Is there a method for locking the metadata that anyone can recommend?
Anyone with an editor can open a TIFF and save it again without the metadata. I don't think there is any way to lock the metadata from being stripped out.
You could look at digital watermarking, such as Digimarc
The only method I've found is to use a very old technique. It was used during the American Revolution by none other than George Washington himself, as well as his compatriots. It's known as STEGANOGRAPHY. There are many free programs available through a Google search. Pick one that suits you.
These programs add small files to the image itself. It can be text, QR code, another image such as a copyright, or whatever else you want to put into it. These tiny files are "embedded" into the image, not attached as Metadata is added as a sidecar. It cannot be seen or removed unless you have the same program and password which YOU add when YOU create it.
I've tested it on many Photo-Hosting sites and Google Plus Photos.
Create, upload, then download from the uploaded image site. Open and run your steganography program to locate the hidden text/files and reveal the contents which were missed by website strippers & rippers! Enjoy!