Whether it's photos of people, buildings, or other copyrighted or trademarked items, the key concept you need to always have at the front of your mind is "association." Does the person or thing in the photo imply he or it is an advocate or sponsor for an underlying idea or product? The stronger the implication of this kind of advocacy, the more likely that someone can draw an "association" between the photo subject and that product or idea....in some states in the USA, people are entitled to be compensated for using their "likeness" for purposes of promoting a product, idea, political or religious view (or to imply support for any of those things). .. while the law may be clear on this for any given state, the real question to ask is still whether a given use of someone's like[ness] is a "commercial use."
Similarly to advocacy, there's the question of whether you may be using "features" of a person or thing—such as whether they are well-known celebrities or iconic logos.... This is similar to the "association" concept, but rather than suggesting that they are "advocates or supporters" of an idea, the use of the image could be exploiting their inherent recognizability and "goodwill" to enhance the perceived value of a product or idea.