1. An image processing apparatus comprising: printing equipment that prints an image on a recording sheet; an image data scaling circuit that scales image data including a tint image in which a concealed character appears from its background area after scanning by a scanner, and outputs the scaled image data to the printing equipment; a scaling factor acquiring unit that acquires a scaling factor specified for scaling performed by the image data scaling circuit; a tint image storing unit that stores predetermined tint images having patterns; a scaling appropriateness judging unit that judges based on a printing resolution of the tint image, a printing resolution of the background area and a scanning resolution of the scanner, when the image data is subjected to scaling with the scaling factor, whether there is a possibility that the form of the tint image will be inappropriate; and an image data processing controller that, if the scaling appropriateness judging unit judges that there is a possibility that the form of the tint image will be inappropriate, prevents the form of the tint image from being inappropriate by judging whether a pattern of the tint image is the same as a pattern of one of the predetermined tint images stored in the tint image storing unit, and if the pattern of the tint image is the same as a pattern of one of the predetermined tint images, lets the image data scaling circuit perform scaling only on the image data and then combines the one of the predetermined tint images stored in the tint image storing unit with the scaled image data.