I'm very new to the site, just found it yesterday, in fact. I certainly wouldn't mind donating photos to someone else's synth, just to see it work. Perhaps MSFT could give us a place where we could relinquish copyright over the photos we donate and thus could not retract them later.
For instance, I have tons of photos of Walt Disney World, and many of NYC. They were not shot overlapping as this didn't exist then. I'd be happy to donate them even though I am a pro, they were taken for fun, and I certainly don't mind sharing them.
So let's say that one person is doing a synth on WDW, or even just an attraction there, all those interested would donate to, say, Magic Kingdom, or Animal Kingdom, or the resorts, or whatever. Believe it or not there are many, many people who have not been there, just as I have not been to Italy or Hawaii yet. What the marvelous syncs do is let people experience these places in breathtaking detail, and I think it is stupendous!