IMAGE PROCESSING APPARATUS AND SYSTEM AND CONTROL METHOD THEREFOR, IMAGE DATA PROCESSING METHOD, IMAGE FORMING APPARATUS AND CONTROL METHOD THEREFOR, CONTROLLER THEREFOR, AND STORAGE MEDIUM STORING THE CONTROL METHOD FOR PROCESSING IMAGE DATA HAVING DIFFERENT PRINTING ATTRIBUTES

An image processing system having a plurality of image forming apparatuses and a method thereof separate a group of image data to be printed into a plurality of groups and transmitting the groups to the plurality of image forming apparatuses. A first image process is executed on the image data to be transmitted, and depending on printing attributes of the image forming apparatuses to which the image data are to be transmitted, a second process, which can be the same as or different from the first process, is executed. Further, the image data having the first attribute are formed on sheets from a first feeding unit while sheets from another feeding unit are inserted into the sheets with the first attribute at pages corresponding to image data of the group of image data having the second attribute.