1. An image erasing apparatus comprising: a scanning unit configured to scan an image on a sheet and a mark printing area on the sheet; an erasing unit configured to erase the image from the sheet; a marking unit configured to print a mark on the sheet; and a control unit configured to: determine a number N of the marks printed on the sheet from scan results of the mark printing area scanned by the scanning unit, determine an image position from scan results of the image scanned by the scanning unit, and determine a position of the mark to be printed on the sheet by the marking unit, wherein the determined position is at a first position (N+1)*x+y or at a second position (N+2)*x+y, depending on the determined image position, where x is a predetermined interval between the printed marks and y is a predetermined distance from the first mark to an edge of the sheet.