In this paper, we propose an appearance-based nude image detection system. The proposed system is novel in that shape information is used to classify the nude images, and detect small nude images in a large background image. First, the proposed system finds skin regions using texture characteristics of the human skin, which then generates the skin likelihood image. Since the skin likelihood image contains shape information as well as skin color information, we used the skin likelihood image as a high level feature to classify the nude images. The image feature vector (resized skin likelihood image) is used as an input to a nonlinear-SVM. Experimental results show that the proposed system can achieve an excellent classification performance. Additionally, the proposed system can detect small nude images in a large image.