Are libraries legally required to obtain photo releases from all patrons (children's parents, teens, adults), even if we don't name those patrons before publishing photos to our social media accounts and/or press releases?
This is a huge question. To answer it, let’s start with where the mania over image releases comes from.
New York Civil Rights Law, §50, states:
A person, firm or corporation that uses for advertising purposes, or for the purposes of trade, the name, portrait or picture of any living person without having first obtained the written consent of such person, or if a minor of his or her parent or guardian, is guilty of a misdemeanor.
In this age where every “click” and post is potentially monetized (and thus “advertising”), this rule is tough to advise on. If I post a picture of my sister on Facebook, and her smiling face helps Facebook get attention for a sidebar advertisement, can she fulfill a threat made back in 1987 to get me in “sooooooooo much trouble?” Not quite. But if I create an ad for an event to be held at my law firm, and I use someone’s image without permission, that could be problematic.
The next layer of concern could come from Facebook itself. As they say in their “Terms,” users may not:
…do or share anything:
So, if my sister alleges that I have “violated her rights,” by posting her picture, am I risking my Facebook account, too?
A lot of this comes down to how Civil Rights Law §50 is being applied these days. As of this writing, I did not find any case law where simply posting an image to Facebook violated §50. Further, recent case law gives insight into what the courts will consider to be “advertising.”
“Under Court of Appeals precedent, the statute is to be narrowly construed and strictly limited to nonconsensual commercial appropriations of the name, portrait, or picture of a living person. A use for advertising purposes has been defined as a use in, or as part of, an advertisement or solicitation for patronage.” 
This sounds helpful, until you starting thinking that, in the world of Facebook, everything is only one degree from being an advertisement. So how does a library post photos of patrons using their library without losing sleep at night?
The 2013 case of Leviston v. Jackson is instructive. In Leviston, a woman sued the rapper 50 Cent for posting a sex tape (not made for commercial use) featuring her on his unmonetized web site. During his testimony, 50 Cent stated that he posted the video to antagonize an opponent in a rap war. During his testimony, 50 Cent admitted that rap wars are conducted in part to test the mettle of different rappers, and to bring attention to the combatants. The judge, seizing on this admission that rap wars are in part for “attention” (of the commercial variety) refused to dismiss the Plaintiff’s claim.
So, if your public library is at war with the association library across town, or fighting a budget battle, and you would like to post pictures of patrons claiming “Our Books Our Bigger!” your library should get written image releases. If, however, your not-for-profit library is simply publicizing “new hours!”, the person whose image you use would have a very weak claim (if they had a claim at all).
That said, in general, it is a good practice for libraries to get image releases whenever possible. First, you never know when you might snap the perfect picture to illustrate why a new resources or a bigger budget would really help your mission. Second, asking for permission to use a person’s image will emphasize your library’s respect for personal privacy and patron confidentiality. And finally, by memorializing permission to use an image, you reinforce the patron’s connection to the library…and generate a great record for the archivist who will be trying to catalog your photos in 2118!
Thank you for your question.
 Leviston v. Jackson.