1. An image processing system comprising: a display apparatus; an image capturing apparatus; and an image processing apparatus, the display apparatus comprising a display unit that displays an image on a display medium, the image capturing apparatus comprising an image capturing unit that outputs a captured image obtained by imaging a subject, and the image processing apparatus comprising: a first acquiring unit that acquires a first pattern image including a prespecified pattern for being displayed on the display medium by the display unit; a second acquiring unit that acquires, as a second pattern image, a captured image obtained by capturing an image obtained by displaying the first pattern image on the display medium with the display unit, the capturing being performed by the image capturing apparatus from a desired position except the front of the display medium; and an image processing unit that compares the first pattern image with the second pattern image, and deforms a target image according to a result of the comparison.