1. An image processing apparatus comprising: an output processing section for executing an output process based on an image data obtained by reading a document image; a storage section in which a description of the output process to be executed by the output processing section is stored in relation with a stored image; and a controller capable of performing operations of: determining whether or not the document image is similar to the preliminary stored image based on the obtained image data; when determining that the image is similar to the stored image, reading out the description of the output process stored in relation with the stored image from said storage section; and controlling the output process to be executed by said output processing section in accordance with the read out description of the output process, the image processing apparatus further comprising: a features storage section for storing features of stored images; a features calculating section for calculating features of the document image based on the obtained image data; and a comparator section for comparing between the calculated features and the features of the stored images, wherein said controller is further capable of: determining whether or not the document image is similar to the stored image based on the comparison by the comparator section, and the image processing apparatus further comprises: a region extracting section for extracting a plurality of regions composed of identical factors from said document image; and a centroid calculating section for calculating the centroid in each of the extracted regions, wherein the features of the document image are calculated based on the centroid.