An information processing system adds density information to a first specific region of a document sheet represented by image data, the density information being indicated by a reference density lower than a density index value derived based on densities of pixels included in the image data. The system adds predetermined restriction information to the image data, the restriction information being indicated by a density equal to or higher than the reference density. The system acquires, as a determined density, a density of the first specific region. The system determines, based on the image data, whether a second specific region that is a part or all of a region of the document sheet, includes the restriction information indicated by a density that is equal to or higher than the determined density. If so, the system restricts a specific process concerning the image data from being executed.