An image processing apparatus includes a forming unit configured to form, on a sheet, a pattern from which at least two lines each connecting two points located at positions parallel to a conveyance direction of the sheet are detectable, a detection unit configured to detect, from the pattern formed by the forming unit, at least two lengths of lines each connecting two points located at positions parallel to the conveyance direction, and an acquisition unit configured to acquire a correction value used when correction is performed so that there is no difference between the lengths of a plurality of lines detected by the detection unit. The forming unit forms an image obtained by correcting a corrected image to be output using the correction value acquired by the acquisition unit.