1. An event detection apparatus comprising: at least one processor and memory coupled to each other and cooperating to act as: an input unit configured to input a plurality of time-sequential images; a first extraction unit configured to extract sets of first image samples, the sets of first image samples composed of a plurality of layers, wherein each layer from the plurality of layers corresponds to a different sampling interval from a first time range of the plurality of time-sequential images, wherein each set of first image samples is composed of a plurality of image samples; a second extraction unit configured to extract sets of second image samples, the sets of second image samples composed of a plurality of layers, wherein each layer from the plurality of layers corresponds to a different sampling interval from a second time range of the plurality of time-sequential images, wherein each set of second image samples is composed of a plurality of image samples; a dissimilarity calculation unit configured to calculate a dissimilarity between a set of the first image samples and a set of the second image samples that have the same sampling interval, for each layer from the plurality of layers; and a detection unit configured to detect an event from the plurality of time-sequential images based on the calculated dissimilarity for each layer from the plurality of layers.