1. An image processing device comprising: an image group generation unit that uses a dictionary storing a plurality of patch pairs including a degraded patch which is a patch of a degraded image obtained by degrading a predetermined image and a restored patch which is a patch of said predetermined image in such a manner that the degraded patch and the restored patch are associated with each other to generate a plurality of restored image candidates including a plurality of different contents that may be an original content of an input image from said single input image; a reliability degree calculation unit that calculates a degree of reliability of each of the restored image candidates generated by said image group generation unit, generates a reduced-quality image from said restored image, and calculates said degree of reliability on the basis of a difference between said reduced-quality image and said input image; and an image selection presenting unit that selects and outputs said restored image candidate on the basis of said degree of reliability.