Photographs are routinely traded and uploaded to devotee sites on the internet and also compiled onto cd's as collections and are sold worldwide.

Could YOUR prosthetist be a devotee?  Sure.  The industry currently does not have any screening process in place to identify these people so the person casting your arm or leg, or touching your child could be a devotee.

How do you guard against this?  I don't think you can really, other than to interview your potential prosthetists VERY carefully, check backgrounds and follow your instincts. 

You (or your child) do not have to be alone with a prosthetist, technician or other medical provider unless you agree.  You can have a spouse, friend or anyone else you want with you for the casting and fitting procedures if you wish.  If your prosthetist balks at this, take that for what it is.  If you feel something is wrong, LEAVE (or remove your child).

Also, NEVER consent or allow photographs to be taken of yourself (or your child).  You are under NO obligation to "show other amputees how well you can walk/use the component" etc.  If you are that good with your prosthesis and someone wants you to show another amputee, if you are interested, have them invite that amputee to the facility where you can demonstrate in person.

Remember, you have all the rights in this situation. 

Of course, NOT ALL prosthetists are devotees, hacks or egomaniacs. 

MOST are highly ethical, conscientious, qualified and capable individuals who are appalled that anyone would abuse their position.  But it is the few that do not have the same ethics as the rest of us that you have to be aware of.