Phototherapy could fairly be defined as an application of one specific medium and material in art therapy. Since digital cameras and mobile phones have become more and more popular in recent years, the concept and profession of phototherapy has drawn much attention from mental health professionals. This article primarily focuses on the literature review of definition, concept, principle and application of phototherapy. The content includes the projective process of photography and working with a variety of photos clinically: "self-portrait photos," "photos taken by others," "photos taken by me," "photos collected by me," "family photo albums." The practice of group phototherapy and possible ethical concerns are also included in this text.