Image reader, and method and computer-readable medium for the same

An image reader comprising:

• a document table configured to support a document placed thereon, the document table having:
• a reference point on which a vertex of the document is positioned;
• a first region within which the document is placed, the first region including a margin region, the margin region being defined as a range within a predetermined distance from a reference line in a main scanning direction, the reference line including the reference point and being parallel to a sub scanning direction perpendicular to the main scanning direction;
• and
• a second region positionally different from the first region in the main scanning direction;
• a document cover movable between an open state and a closed state, the document cover being configured to cover an upper surface of the document table when the document cover is in the closed state;
• a reading unit comprising a light source configured to emit light toward the document placed on the document table, the reading unit being configured to perform image reading on a line-by-line basis along the main scanning direction, and output analog data as read data;
• a converter configured to convert the analog data output from the reading unit into digital data;
• a moving mechanism configured to change a reading position where the reading unit performs image reading, in the sub scanning direction by moving the reading unit along the sub scanning direction;
• and
• a controller configured to:
• control the moving mechanism to change the reading position to a particular position in the sub scanning direction;
• acquire specific digital data of the second region through image reading in the particular position with the light source turned off;
• determine an open/closed state of the document cover based on the specific digital data;
• acquire first digital data of the margin region through image reading in the particular position with the light source turned off when the document cover is open;
• acquire second digital data of the margin region through image reading in the particular position with the light source turned on when the document cover is open;
• and
• determine existence of the document in the margin region on the document table, based on a difference between the first digital data and the second digital data.