I am a lawyer, but this is not legal advice. Write me a check, you'll get legal advice.
Those balloons are almost certainly copyrightable works of art and commercially exploiting them could get you in hot water. I'd get a release. Perhaps the people who run the event get a blanket release from participants so they can use photos of the event. You might ask if they can do sublicensing or collective clearance.
Depending on the balloon, some of them might also be considered trademarked or to comprise protectable trade dress, although that wouldn't be as big a problem as copyright infringement in this case.
M
|