If I may.......it is, of course, a question of good manners to request the permission of a FA or crew to take a picture of her/him/them and you should not be surprised if they refuse. I suspect this has happened and its not surprising then, that they might object if that is their wish. Insofar as the use of cameras is concerned I very much doubt that they are construed as a portable recorder since these devices are offered all over the internet as portable audio recorders. In my many years in aviation I have not heard of a camera being bought into question other than above. As for using them during take-off or landing - I cannot see the problem.
It may be noted that a camera can emit tiny amounts of energy via LED panels but the level would so small as to be of no consequence whatsoever.