1. A method for image characterization, comprising: providing an image comprising a plurality of pixels; converting the image into Hue Saturation Value (HSV) model, each pixel comprising a hue level, a saturation level and a brightness level; calculating color levels of the pixels respectively, the color levels comprise hue level, saturation level and brightness level; and determining characteristics of the image according to the calculation result, wherein the step of calculating the color levels of the pixels respectively comprises: for each color level of hue, saturation and brightness: calculating a first ratio of each level to generate a cumulative histogram, the first ratio of a certain level is calculated by dividing cumulative amount of pixels up to the certain level with the total amount of pixels in the image; calculating a second ratio of each level to determine one or more key levels, the second ratio of a certain level is calculated by dividing the amount of pixels of the certain level with the total amount of pixels in the image; and calculating one or more invariant moments of each key level according to the cumulative histogram; wherein the characteristics comprise the one or more invariant moments, wherein the step of calculating one or more invariant moments comprises: generating one or more seed functions by applying the key level with a plurality of horizontal orders and vertical orders to a center moment cumulative function; and generating a plurality of invariant moments corresponding to the key level by combining the one or more seed functions.