Can I source photos off of the web of celebrities for non-commercial purposes? In particular: a theatre wants to project images of celebrities onto the backdrop of their stage as part of a "tribute to the greats" number.
According to US law (and I believe similarly in most areas), commercial use is defined as:
According to 18 USCS § 31, term "used for commercial purposes" means the carriage of persons or property for any fare, fee, rate, charge or other consideration, or directly or indirectly in connection with any business, or other undertaking intended
The important part of that being;
directly or indirectly in connection with any business
Which means you don't necessarily have to directly charge for or financially benefit from something for it to be considered used for commercial purposes.
Also keep in mind that you are probably violating the copyright of the Photographer as well as the celebrity's rights of publication.
Always ask permission.
If you are a non-profit organization and/or the use is educational then you may be able to use the image without permission (under a "fair use" clause), but this doesn't sound like its the case.
I am not a lawyer. This is not legal advice. If you require sound legal advice, contact a legal professional.