The user has a Nikon system camera with remote release cable. The remote release is attached to the accessory contact on the camera. The user operates the remote control with her mouth. To protect the remote release from saliva the user covers it with the finger of a rubber glove.
Unfortunately remote release is only available as an accessory on expensive cameras.
Photography supply store
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See also rollingfstop.blogspot.com/2008/12/camera-mount-for-wheelchair-photography.html (last checked September 2020).
This tip is from 2009