Lens dirt prompting method and system, readable memory medium and mobile terminal

The invention provides a lens dirt prompting method and system, a readable memory medium and a mobile terminal. The method comprises the steps of obtaining a target gray value of a preset area in a currently photographed image, wherein the currently photographed image is photographed by a lens; obtaining a target exposure value in the currently photographed image; judging whether the target gray value is in a gray threshold range corresponding to the target exposure value or not; and sending prompt for prompting a user that the lens is dirty if the target gray value is not in the gray threshold range. According to the lens dirt prompting method and system, the readable memory medium and the mobile terminal provided by the invention, whether the lens is dirty or not can be automatically identified and the user is automatically prompted under the condition that the lens is dirty, so the user does not need to frequently check whether the lens is dirty or not, the experience is good, and the identification precis