1. An electronic device, comprising: at least one image source unit, configured to obtain a series of images; and an image processing unit, coupled to the image source unit and configured to: determine camera states corresponding to the series of images; select first images from the series of images according to the camera states; determine object states corresponding to the first images; divide the first images into a number of groups according to the object states; and select a candidate image from each of the number of groups.