An amateur photographer at a scenic rest stop sees a couple trying to compose a decent photo of themselves with the beautiful river in the background. This happens so often that as he approaches nobody even needs to say a word: They hand him their camera, and then step back so he can take their picture with it.
But in this hypothetical scenario something extraordinary happens: As he takes their picture a commercial airplane doing an emergency landing hits the river in the frame of the photo. So he happens to have pressed the shutter button on what turned out to be a very valuable picture. Let us supposed that a media buyer offers $10k to license the photo. Who owns the copyright to that photo?
On the one hand, the camera owners could argue that the photographer exercised no more "creative expression" than does a tripod or selfie stick. They just didn't have one handy, so they composed the photo and the photographer was just a mechanism to hold the camera and release the shutter. Therefore, they must own the copyright.
On the other hand, the photographer could argue that he "fixed the expression" of the creative work. As an experienced photographer he made subtle decisions regarding framing and timing of the photo that were outside of the control of the couple. Alternatively, if he hadn't been volunteering to photograph the couple with their camera, he could have instead been holding his own camera and captured the valuable element of the photo, which was the serendipitous emergency landing.
Does any law or jurisprudence inform who owns the copyright in this scenario?
If the aforementioned facts suggest it is the couple (and owners of the camera), then let us change one fact: After taking the couple's desired photo, the photographer sees the airplane out of the corner of his eye and, with no time to spare, shifts the camera to capture a separate spectacular photo of the water landing. Does he now have firm claim on the copyright to that photo?
And if so, can the photographer enforce his property rights in the photo, given that it was captured and is stored on equipment he does not own and cannot legitimately possess? I.e., can't the camera owner say, "OK, you own the photo copyright, but I own the medium where you put its only copy, and I will not sell or grant you access to that medium except for the full value of the photo."