Art is where you find it. If you find inspiration alone, on some rock out in the desert that's fine. If you find artistic inspiration in the middle of Times Square at New Years, then that's fine too. It's unique to each individual and calling absolutes is just silly. Each person is different with their artwork, and each person finds creativity according to their own creative needs. Thank god we're not all the same, or else every book would be exactly the same!
Not only that, but how would photographers do their work? I guess they could take still life/nature photos, but I like photos of people, and that's team work. The famous bands, like The Beatles or the Eagles wrote their songs together. Stairway to Heaven was written by more than one person, and that's been called the greatest song ever written.
Anyways, back to the original post, my sister and I co-authored a thing together (I call it a 'thing' because it never really got finished). We dove tailed a story. She wrote a chapter with her own characters, and I wrote a chapter with my characters and eventually, our two groups of people met. It never got finished though. You just need to figure out a format that works between you and the other author. Everyone will go about it differently.
ETA: I didn't realize this was an old thread. Wow, I just looked at the OP date! lol