An image processing apparatus includes a first memory, a data detector, a second memory, a third memory, and a determiner. The first memory stores a reference pattern including a plurality of reference basic units, each of which represents specific minimal information, is superposed on input image data, and represents specific entire information. The data detector detects a basic unit in the input image data based on the reference basic unit included in the reference pattern stored in the first memory. The second memory accumulates a number of basic units detected by the data detector. The third memory stores a predetermined value. The determiner determines whether the number of basic units detected by the data detector and stored in the second memory is equal to the predetermined value stored in the third memory.