ABNORMALITY DETECTION DEVICE, ABNORMALITY DETECTION METHOD, PROGRAM, AND INFORMATION PROCESSING SYSTEM

The imaging unit captures an image using a lens having an effective image circle smaller than the imaging surface of an image sensor. A vignetting amount calculation unit of a detection unit individually calculates, for four corners, a region size of a vignetting region generated in the captured image acquired by the imaging unit , for example. A determination unit detects a change in the region size calculated at the time of focus abnormality detection processing with respect to the region size calculated at the reference time, and determines that a focus abnormality is detected when the change in the region size exceeds a threshold at any of the four corners. This enables accurate detection of focus abnormality.