To solve the problem that a test pattern image can not be accurately read if an image-receiving sheet with the test pattern image printed thereon is not accurately positioned to a scanning face.

When capturing the test pattern image, the following processes are performed. A process (a) is performed for optically reading a printing image formed by printing a test pattern being the test pattern, in which N stages of a belt-like single-color pattern extending in the sub-scanning direction are arrayed in the main scanning direction, and black is arrayed at the first stage, white at the second stage, intermediate color having gradually deeper gray scale density at the stages from the third stage to the (N-1)th stage, and black at the N-th stage with a sublimation type thermal transfer system. A process (b) is performed for selecting scan data, in which all the single-color patterns from the first stage to the N-th stage appear, from among the scanned data corresponding to each read scan line.