1. A method for estimating whether an image is blurred or sharp, the method comprising the steps of: determining an image gradient histogram distribution of at least a portion of the image, wherein such determining includes the steps of dividing the image into a plurality of image regions and determining an image gradient histogram distribution of at least one of the image regions; comparing at least a portion of the image gradient histogram distribution to a Gaussian model, wherein such comparing includes the steps of comparing the image gradient histogram distributions for at least one of the image regions to a Gaussian model and comparing a tail section of the Gaussian model to a tail section of the image gradient histogram distribution; and estimating a defocus blur size of at least a portion of the image.