Abstract: A depth-photographing method of detecting human face or head includes the steps of using the specific light to illuminate the target under an environmental light, receiving and detecting the reflected light from the target with the detector, generating first depth detecting information corresponding to the depth of the target, turning off the specific light, detecting another reflected light from the target, generating second depth detecting information corresponding to the depth of the target, performing the detection/calculation process based on the first and second depth detecting information to generate the appearance of the target, determining if the appearance of the target represents a human face or head, and if yes, generating depth-photographing detection information used to cancel a lock state, thereby avoiding unintentionally entering power saving (or standby mode), speeding up entering the desired power saving or dynamically changing/adjusting the display content.