When selecting photos of people, it is best to avoid using close-up shots of just their mouth or any other body part. Doing so can be seen as objectifying the person, reducing them to a single body part instead of representing them as a whole. Objectification can be seen as offensive and can give the impression that a person is being treated as nothing more than a smile instead of a person.
This is why we recommend using full face photos instead of close-up shots of just the mouth. Photos like these represent the person as a whole, showing their facial expressions and body language, which is a much more respectful way to represent someone. Additionally, it allows the person to be seen in their full context and avoids any potential misunderstandings or offense.