1. An image processing device, comprising: a scanner to scan an image formed on a sheet; a first image obtainer to read and obtain a first image being a processible image formed in a first area, the first area being allocated on the sheet; a second image obtainer to read and obtain a second image formed in a second area, the second area being allocated on the sheet separately from the first area; a judging unit to judge as to whether the second image obtained by the second image obtainer qualifies a predetermined authentication criterion and is identical to a predetermined identifying image; and a function controller to activate a predetermined function of the image processing device, which processes the processible image obtained by the first image obtainer, when the judging unit judges that the second image is identical to the predetermined identifying image.