An image reader includes a reading unit that is configured to read an image on a document sheet to generate read data, a counting unit that is configured to count a number of pixels of the read data having more than a predetermined gray level, a determining unit that determines that the document sheet is blank when the number of pixels counted by the counting unit is not exceeding a threshold value, a display unit that is configured to display the number of pixels counted by the counting unit and the threshold value when the document sheet has been determined to be blank, in a manner that the number of pixels can be compared with the threshold value, and a changing unit that changes the threshold value.