1. A computer-implemented image segmentation method, comprising: receiving, at one or more computing devices, a video image of a dynamic movement of a target object; acquiring, at the one or more computing devices, a full-image optical flow of the video image and a background optical flow of the video image; estimating, at the one or more computing devices, a first displacement of each pixel in the video image based on the acquired full-image optical flow of the video image; estimating, at the one or more computing devices, a second displacement of a background pixel in the video image based on the acquired background optical flow of the video image; comparing, at the one or more computing devices, the first displacement with the second displacement to obtain a foreground region of the target object; extracting, at the one or more computing devices, feature points in the video image in the foreground region of the target object; calculating, at the one or more computing devices, a probability density of the feature points extracted to determine a number of the target objects; performing, at the one or more computing devices, a visual tracking and a movement trajectory analysis on the target object to track the target object; and performing, at the one or more computing devices, a stationary judgment and an image segmentation on the target object according to an interframe displacement of the feature points, an interframe cutting window similarity, and a tracking box scaling.