1. An apparatus, comprising: a hardware computing device that implements: a feature data generation unit for determining feature points of at least a first image and a second image, and generating feature data including pieces of feature point orientation information for the respective feature points, and a relation analysis unit for analyzing a correlation between the first image and the second image using the feature data, by at least: determining pairs of corresponding feature points between the first and second images using the feature data generated by the feature data generation unit; and determining a first difference between a first feature point of the first image and a corresponding second feature point of the second image, determining a probability that the first difference is observed using a probability function of a standard normal distribution having a predetermined mean and a predetermined standard deviation, and determining the estimate of the reliability of analysis of the correlation between the images based on a comparison of the probability that the first difference is observed to a threshold value.