The paper is to explore the potential problems, such as cultural issues, in the art therapy assessment and picture analysis through literature review. The overemphasis on clients' art as diagnostic tool may be potentially problematic, because it may cause the danger of having an inhibiting effect on the clients' artistic development, creativity and imagination. The article also presents a case study in the model of open studio to illustrate the importance of aesthetic quality of artworks done in the context of art therapy for assessing the outcome. The discussion of how art therapists can incorporate the concept of ”the third hand” into the practice to create a safe space and prepare a variety of materials, as well as utilize the ability of artistic sensibility and aesthetic empathy to assist clients in artistic expression is included.