1. An image processing device, comprising: a scanner configured to scan an image formed on a sheet; a first image obtainer configured to obtain a first image scanned by the scanner from a first area, the first image being a processable image, and the first area being allocated on the sheet; a second image obtainer configured to obtain a second image scanned by the scanner from a second area, the second area being allocated on the sheet separately from the first area; and a control device configured to: judge whether the second image obtained by the second image obtainer qualifies a predetermined authentication criterion and is identical to a predetermined user-identifying image which is registered in association with a user and a predetermined function of the image processing device, the predetermined function being configured to process the first image obtained by the first image obtainer and being allowed to be activated by the user; and activate the predetermined function of the image processing device, which processes the first image obtained by the first image obtainer, when judgement is made that the second image is identical to the predetermined user-identifying image, wherein the second image obtainer completes obtainment of the second image from the second area prior to activation of the first image obtainer; and wherein the first image obtainer is activated to start obtaining the first image when the judgment is made that the second image obtained by the second image obtainer is identical to the predetermined user-identifying image.