1. An image processing apparatus comprising: a memory; and a processor coupled to the memory which executes a process including: detecting a face area and an eye area from images that are sequentially input; calculating, between two of the images, a first motion vector in the face area and second motion vectors, each of the second motion vectors corresponding respectively to each of a plurality of blocks obtained by dividing the eye area; calculating, for each pair of the images, a plurality of similarities by calculating a similarity between the first motion vector and each of the second motion vectors, wherein each of the plurality of similarities is calculated based on a cosine value of an angle between the first motion vector and one of the second motion vectors; calculating an average similarity based on the calculated plurality of similarities; and determining whether a part of blinking has occurred by comparing the average similarity with a threshold.