This paper presents a new adult image identification system. We propose the online skin tone sampling mechanism based on face detection. The object detection based on machine learning approach is used to locate the face region in the target image. According to the face color information, the skin chromatic distribution is extracted to detect the skin objects in the target image. The texture feature, coarseness, is also utilized to acquire the more accurate skin regions. Then, the back propagation neural network is used to integrate several low-level and reliable geometrical constraints into a classifier to inspect the skin regions further. Finally, the mug shot exclusion procedure is applied to promote the system performance. The experimental results show our method is satisfactory for adult image detection.