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 that generates a projected waveform of the reference image and a projected waveform of the target image; a feature volume extraction unit that extracts feature volumes from the projected waveform of the reference image and the projected waveform of the target image and generates feature volume data of the reference image and feature volume data of the target image, respectively; a feature volume correlation unit that correlates the feature volume data of the target image with the feature volume data of the reference image; a correction value calculation unit that calculates correction values in accordance with geometrical distortion between the reference image and the target image based on a result of correlation of the feature volume data of the target image with the feature volume data of the reference image; and a collation unit that collates the target image with the reference image by using the correction values.