1. An image processing apparatus for collating a target image as a subject of inspection with a reference image, comprising: a projected waveform generation unit for generating a projected waveform of the reference image and a projected waveform of the target image; a feature volume extraction unit for extracting feature volumes from the projected waveforms and generating feature volume data respectively; a feature volume correlation unit for correlating the feature volume data of the target image with the feature volume data of the reference image; a correction value calculation unit for calculating correction values in accordance with geometrical distortion between the reference image and the target image on the basis of a result of correlation of the feature volume data; and a collation unit for collating the target image with the reference image by using the correction values.