1. An image processing method, comprising: capturing two images; detecting a difference between the two images; reserving one of the two images when the difference is less than a preset threshold; detecting feature information of one of the two images; performing definition-related treatment for the image having detected feature information; and reserving a clear image according to the definition-related treatment; wherein, before performing the definition-related treatment, the method further comprises cropping the image having the detected feature information so as to increase a percentage of the detected feature information to the whole image; wherein performing the definition-related treatment, and reserving the clear image according to the definition-related treatment comprises at least one of: graying the cropped image; calculating a gradient value of the grayed image; outputting a grayscale image which comprises edge information; setting a grayscale image threshold as a definition criterion according to the grayscale image; binarizing the cropped image; obtaining a binarized threshold corresponding to the binarized image; determining that the image is clear and reserving the image if the binarized threshold corresponding to the binarized image is less than the grayscale image threshold; and graying the cropped image; calculating a gradient value of the grayed image; outputting a grayscale image which comprises edge information; using a total sum of white pixel points of the edge information of the grayscale image or a percentage of the edge information to the whole image as a definition criterion; binarizing the cropped image; obtaining a total sum of white pixel points of the edge information in the binarized image or the percentage of the edge information to the whole image; determining that the image is clear and reserving the image if the total sum of the white pixel points of the edge information in the binarized image or the percentage of the edge information to the whole image is less than the definition criterion.