If you don't have access to the source code then you don't know what it's doing. If there's economic incentives to take my picture and tie my face to my name then I'm going to assumed "trust us, it's anonymous" means at least "we buy and sell your data".

If you'll grant there are people in power who would want a surveillance state and businesses routinely sell data to governments then you don't get to dismiss this out of hand. We have to draw then line somewhere, even if marketing people with a stalker mentally don't see the line.