Portraiture in art therapy

For many years I have been exploring the human face in my artistic work. Sometimes I used photographs sometimes someone sat for me so that they could hang the picture in their home or give it away as a gift. Occasionally I used a friend's face as inspiration for a theme I was working on. When I began painting patients in an art therapy setting I wondered how the process of portraiture might influence the relationship between therapist and patient and when this method might be problematic.