1. A test method for image sharpness, which can instantly determine the sharpness of an image after an electronic camera device has captured the image, comprising the following steps: dividing said image into multiple blocks with each said block composed of multiple pixels; summing up the sharpnesses of said pixels having higher sharpnesses inside each said block to obtain the sharpness of the related said block; summing up the sharpnesses of said blocks having higher sharpnesses to obtain an estimated sharpness of said image; and comparing said estimated sharpness with a threshold value to determine whether said image is sharp.