An image processing apparatus including, a light source for reading for applying light onto an original to read, a light source for erasing for applying light of specific wavelength onto the original to decolorize image area, having been printed with color-changing agent having characteristic to become colorless by the light, a reading section for receiving reflected light from the original, an output section for outputting image data of the original, and a control section configured to compare first image data obtained by applying light from the light source for reading to the original, and second image data obtained by applying light from the light source for reading again to the original after applying light from the light source for erasing to the original, to determine whether the agent has been used in the image, and control at least either the reading operation or the output operation based on that determination.