Short and swee...
It is my understanding that whether or not you have someone pose for you, you should not post or otherwise use their image for profit without a signed release.
Note: Profit can mean money, notoriety, fame or any gain by you.
If however you were to take a photo of a crowd or otherwise unrecognizable people (you have not zeroed in on any individual or assembly) you can go ahead and sell the image. Now along comes JQ Public and says, "I did not give you permission to sell my picture", you are still OK since there is no way to prove you sold the photo just to sell JQ's image.
If you were to take a picture of a group of bowlers recognizable as the "Jets Bowling Team" for example, you do need a signed release.
I believe this comes to play when you publish, but not for profit, photos of unknown subjects found on film in a camera you purchased.