1. A method for extracting an image from a video, comprising: acquiring a target image corresponding to a target object in a T th frame; acquiring original image resolution S 0 of the T th frame, wherein T is a positive integer; performing at least one image analysis processing on the T th frame, wherein the image analysis processing comprises foreground extraction, target detection, and target tracking; determining a resolution parameter P of the target image, wherein the resolution parameter P is a ratio of an original quantity S i of pixels in the target image to a quantity of pixels in the target image after the at least one image analysis processing has been performed on the T th frame; obtaining an extraction resolution S 1 according to the original image resolution S 0 and the resolution parameter P; and extracting an image of the target object in a (T+1) th frame according to the extraction resolution S 1 , wherein determining the resolution parameter P of the target image comprises acquiring the original quantity S i of pixels in the target image, and wherein performing at least one image analysis processing on the T th frame comprises: performing foreground extraction on the T th frame; acquiring a post-foreground extraction quantity of pixels in the target image after performing foreground extraction on T th frame; performing target detection on the T th frame; acquiring a post-target detection quantity of pixels in the target image after performing target detection on T th frame; performing target tracking on the T th frame; acquiring a post-target tracking quantity of pixels in the target image after performing target tracking on T th frame; determining a minimum pixel quantity S min among the post-foreground extraction quantity of pixels, post-target detection quantity of pixels, and post-target tracking quantity of pixels; and determining the resolution parameter P of the target image according to the original quantity S i and the minimum pixel quantity S min .