I've seen variants of this question covered on many sites but I can't find an answer specific to fine art sales. I know that I need a model release if my picture will be used as stock photography (promotion, advertising, etc). But what if I take a picture of a street performer and then want to sell that photo to someone to hang in their home or office? It wouldn't be used to promote a product but it would still be a commercial sale.
Is a release needed for this situation?
If there are people in the image that are readily identifiable, yes. This is true for any image that will be used in promotion of something else. In your case things become a little muddy and ultimately comes down to the, "what-if?"
"What-if," the street performer walked into an office and saw a photo of him/herself and thought, "I never signed a model release for that. Dang, I'm ticked off!" and then proceeded to find a lawyer, hunt you down and drag you to court. Then the judge happened to be haunted by a terrible school photo from his early childhood and was like, "this court finds that you owe street-performer cash for mental anguish!" Probably will never happen.
As photographers we are allowed to photograph anyone and anything we can see with our naked eye on or from public property. This law stems from the protection of press freedoms and extends through freedom of speech. In this regard, to make a photograph of a public performance artist in a public place and then charge money for prints, you do not need a model release. However, you should always have a model release with you. You never know when you will find that amazing image that Coca-Cola wants to pay you 10k for.
*of special note...when photographing a piece of public art wherein the art is the central focus of the image, you do need permission from the artist to resale the image. However, if the artwork appears in the image as a part of your composition, you're alright.
If your photo contains recognizable faces or private property you must next attach a signed model or property releases if you wish to sell it as commercial stock photography.
In the event that your photograph contains conspicuous appearances or private property you should next append a marked model or property discharges on the off chance that you wish to offer it as business stock photography.