I do not understand your comparison of a Cellphone camera to a Debt note... Is that a valid analogy? I believe that the bad uses of the camera are only if the camera is used for an illicit purpose. I don't know if anyone else has asked a question like this...
I believe that the reason to forbid keeping a cancelled debt note is that, even if we don't intend to claim the money again, we are violating a security measure that ensures our neighbours right, Because if we keep it, he depends only on our good will. So the same would apply to keeping a copy of the keys to his house, even if we don't intend to use it. Since some persons would not allow me entering his home, institution or office with a cam, or a recorder as a security measure to protect his privacy, but would, perhaps unwittingly allow me to use a cell phone with cam and recorder, just becasuse it's unpolite and quite a problem to ask me to leave the cell outside, I thought that he might be somehow forced to drop a security measure and relying only on my good will. Thence I found an analogy.
But, since other cams are generally carried in the streets and public places, and have also a potential to be misused, and the question has never arisen, I imag¡ine that's it's quite unlikely to be a problem with cells. Especially since I nearly never enter a place where cams are forbidden.