I think a more apt analogy what be if photographer inadvertently leaves a camera on the ground, and I use it to take selfies. Who owns the copyright to my selfies, me or the owner of the camera?
You would. But the camera owner owns the equipment and all the physical materials your copyrighted work is embedded in, so he or she owns the only physical copy; you'd find it hard to make yourself rich with it without the photographer's permission.
And of course, the act of taking the picture might conceivably constitute some other crime, such as criminal damage (if a film camera, you're rendering good film unusable) or computer misuse (if digital), so in general, this selfie-taking exercise would be even less of a smart move than usual.
