1. A paper sorting apparatus configured to determine a recycling classification of a printed paper, comprising: a processing unit; a scanning unit configured to scan an image printed on the printed paper; memory having executable instructions stored thereon that, when executed by the processing unit, cause the processing unit to function as a printing ratio determining unit that determines a printing ratio as a ratio of the number of colored pixels to the number of pixels of a whole area of the image scanned by the scanning unit; a classification determining unit that determines a recycling classification of the printed paper between recyclable and unrecyclable based upon whether the printing ratio determined by the printing ratio determining unit is less than a predetermined value; and a sorting assist unit that assists sorting of the printed paper in accordance with the recycling classification determined by the classification determining unit, the sorting assist unit including an output unit that outputs information, onto a medium other than the printed paper, that identifies the printed paper and its recycling classification; and a paper feeding unit configured to feed the paper with the printed image thereon to be scanned by the scanning unit, wherein the sorting assist unit includes a paper feeding stopping unit that stops a paper feeding operation being executed by the paper feeding unit based upon the recycling classification determined by the classification determining unit.