Joe, I don't think this really matters much in this case...sort of off topic, but you're not trespassing until you have been asked to leave and refuse to, or if you enter a property after being warned not to. If someone comes into your garage (after being allowed or invited by you) and starts taking pictures, you have every right to ask them not to and to ask them to leave if they continue to take pictures. If they refuse, then they are trespassing. If that didn't happen, then no trespassing took place. You can't allow someone onto your property, then suddenly decide they are trespassing. You have to ask them to leave and warn them not to re-enter the property, then they have to violate that before there is trespassing. If someone comes onto your property unauthorized (without being allowed on the property or invited on the property), then they are trespassing even without being warned. If they enter a building or structure unauthorized, that would be a more serious crime, either burglary or B&E depending upon the state and how the statutes are written.
However, you are right...if there was an agreement with the photos, then the agreement should be adhered to. Unfortunately, it sounds like even though this was a quasi-business agreement, nothing was in writing.