Q: We're reviewing a new movie (or a new song, video game, TV show, book, etc.). Can we use an image we found online as an illustration?
A: Yes, but you have to be selective. As a general rule, most of material that you find online — whether it's a photo, a story, music, etc. — is protected by copyright. If you want to use it, you'll first need to obtain permission from the copyright owner (which may or may not be the operator of the website where you find the material).
There is, however, one important exception called Fair Use. The fair use exception allows you to use limited portions of otherwise copyrighted material without permission when engaged in news reporting or when publishing commentary or reviews.
To qualify, the copyrighted material that you use must be very closely tied to a bona fide news story, news survey, commentary or review. For example, in reviewing the latest Jennifer Lawrence movie, the fair use exception would allow you to use a still image from the movie or a scaled down image of the movie's promotional material (for example, the movie poster) taken from the movie's official website to illustrate your review. Fair Use would also not apply if you were to use a candid photo of Lawrence from People Magazine or or some other third-party website that is unconnected to the movie you're reviewing. A candid photo of Lawrence walking down a Los Angeles street taken by a People Magazine photographer really has nothing to do with the movie and would likely not qualify as a Fair Use. If you want to use it, you'd need to obtain People Magazine's permission.