It’s good to be cautious. There’s definitely a gray area, but some authors have been sued for misusing a photo.
According to Shutterstock:
“YOU MAY NOT portray any person depicted in Visual Content (a “Model”) in a way that a reasonable person would find offensive, including but not limited to depicting a Model: a) in connection with pornography, ‘adult videos’, adult entertainment venues, escort services, dating services, or the like; b) in connection with the advertisement or promotion of tobacco products; c) in a political context, such as the promotion, advertisement or endorsement of any party, candidate, or elected official, or in connection with any political policy or viewpoint; d) as suffering from, or medicating for, a physical or mental ailment; or e) engaging in immoral or criminal activities.”
There are lots of articles online about this. But if you really want some legal advice, just hire/consult with an IP attorney.