Have you ever taken photos at library programs? If you're a librarian, have you then used those photos for promotional purposes (e.g., posting on social media, such as Facebook, Twitter, Pinterest, Flickr, Tumblr, Instagram, or elsewhere)? Do the images include identifiable patrons who attended or participated in the programs? If so, you should probably have gotten their permission before publicly displaying the photos.
In tort law, appropriation, a form of invasion of privacy, occurs when someone uses another person's name or likeness without permission to gain some benefit. For example, if a library used a picture of a patron attending a library program in a brochure (or online) to promote future programs, and the library failed to secure that person's permission to use his/her likeness, then the library could be liable for the tort of appropriation. (I'm paraphrasing this paralegal torts textbook's definition.)
Are most folks going to file a lawsuit against a library over unauthorized use of their photograph? Probably not. Litigation is expensive. If someone is unhappy about his/her likeness being used without consent, s/he will most likely just ask that the picture be removed. But somebody out there would sue, and no library wants to be a defendant.
There's a simple solution: Have patrons sign a liability release granting the library permission to use their images or likenesses for promotional (or other) purposes. Where can you find such a form? How about this? I found it on the Internet a few years ago and have revised and updated it with some boilerplate legalese.
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Of course, we're not giving legal advice here. (Standard disclaimer landing on runway #1 ....) You should consult with your library's attorney to determine if this, or any other, form is legally sufficient for your needs. (It's italicized, so it must be serious.) Have your library attorney draft one. That's your best bet. We provide this example simply as an illustration of what might be workable under suitable circumstances. Use at your own risk. (Our attorney made us say all that. Sorry.)
Having patrons sign a release form protects the library and its employees and board members from civil liability. Library budgets are strained enough; nobody wants to deplete them further by having to pay damages in some lawsuit.