An image processing system for executing an image process for correction to image data contained in a print job, comprising: a first image detector (3, 73a) which is configured to compare first image data for reference with second image data to be processed, and detects a first pixel group from the second image data, the first pixel group having coordinates and constituting pixels, which are the same as those of a pixel group of the first image data; a second image detector (3, 73b) which is configured to compare the first image data with the second image data, and detects a second pixel group from the second image data, the second pixel group having a coordinate in a main scanning direction orthogonal to a paper conveying direction, and constituting pixels, which are the same as those of the pixel group of the first image data, but having a coordinate in the paper conveying direction different from a coordinate of the pixel group of the first image data; a storage unit which is configured to store reusable region information including information relating to the first pixel group and the second pixel group for each of image data contained in a print job; and an image processor (4,82) which is configured to execute an image process for correction to the image data to generate corrected image data based on state information relating to the main scanning direction of a printer engine for forming an image on a recording material, and the reusable region information, wherein: upon generation of the corrected image data from the second image data, the image processor (4,82) reuses a result of image process for correction to the pixel group of the first image data at the same coordinates for a region of the first pixel group of the second image data, reuses a result of image process for correction to the pixel group of the first image data on the same axis in the paper conveying direction for a region of the second pixel group of the second image data, and newly executes the image process for correction to a region of other pixel groups which have not been detected as the first pixel group and the second pixel group of the second image data. a first image detector (3, 73a) which is configured to compare first image data for reference with second image data to be processed, and detects a first pixel group from the second image data, the first pixel group having coordinates and constituting pixels, which are the same as those of a pixel group of the first image data; a second image detector (3, 73b) which is configured to compare the first image data with the second image data, and detects a second pixel group from the second image data, the second pixel group having a coordinate in a main scanning direction orthogonal to a paper conveying direction, and constituting pixels, which are the same as those of the pixel group of the first image data, but having a coordinate in the paper conveying direction different from a coordinate of the pixel group of the first image data; a storage unit which is configured to store reusable region information including information relating to the first pixel group and the second pixel group for each of image data contained in a print job; and an image processor (4,82) which is configured to execute an image process for correction to the image data to generate corrected image data based on state information relating to the main scanning direction of a printer engine for forming an image on a recording material, and the reusable region information, wherein: upon generation of the corrected image data from the second image data, the image processor (4,82) reuses a result of image process for correction to the pixel group of the first image data at the same coordinates for a region of the first pixel group of the second image data, reuses a result of image process for correction to the pixel group of the first image data on the same axis in the paper conveying direction for a region of the second pixel group of the second image data, and newly executes the image process for correction to a region of other pixel groups which have not been detected as the first pixel group and the second pixel group of the second image data.