1. An image processing method of improving human face recognition, applied to a human face recognition system, the image processing method comprising: capturing an image including a human face; executing a face detection in a predetermined area of the image; adjusting an exposure value of the predetermined area to an expected value when the face detection does not recognize the human face; executing the face detection and analyzing an image information in a face area of the image when the exposure value of the predetermined area reaches the expected value; selecting a model parameter and an image adjusting parameter corresponding to the model parameter according to the image information and processing the face area of the image; and outputting a processed image to the human face recognition system.