1. An event detection apparatus comprising: an input unit configured to input a plurality of time-sequential images; a first extraction unit configured to extract sets of first image samples according to respective different sample scales from a first time range of the plurality of time-sequential images based on a first scale parameter; a second extraction unit configured to extract sets of second image samples according to respective different sample scales from a second time range of the plurality of time-sequential images based on a second scale parameter; a dissimilarity calculation unit configured to calculate a dissimilarity between the first and second image samples based on the sets of the first and second image samples; and a detection unit configured to detect an event from the plurality of time-sequential images based on the dissimilarity.