>>4141Voice is the only realistic option there is aside from pictures of body parts, which I'd be against. If voice changers are such a problem, just have people change their voice or sing a line. I do think that voice changers are very detectable though.
(By the way, ccanons, make sure your phone cameras have location turned off so that your geolocation isn't recorded with each pic you take. It is on by default on all phones now and it makes it easy to find you.)