1. An image quality evaluation system comprising: a difference calculator that calculates a difference between data representing a feature of a pixel group comprised of at least one pixel making up a first image, and data representing a feature of a pixel group comprised of at least one pixel making up a second image; a degree-of-focused-area calculator that decides a focused area in the image having a predetermined feature using at least one of said first and second images, and calculates a degree of focused area indicating the degree of being said focused area; a difference weighting section that applies weighting to the difference in feature for a pixel group falling within said focused area based on said degree of focused area; and an image quality value calculator that calculates an image quality value for said first image based on the difference weighted by said difference weighting section.