An image processing device includes an obtaining unit obtaining image data of images; a dividing unit dividing the obtained image into N blocks; a designation unit sequentially designating the M blocks among the N blocks as the blocks to be updated; a histogram generation unit generating histograms of the obtained image data; a histogram storage unit sequentially updating and storing the generated histogram; a change determination unit determining a change in the obtained image, on the basis of the degree of similarity between the histogram of the generated M blocks and the histogram of the M blocks in the past corresponding to the generated M blocks which are stored; a normalization determination unit determining whether or not to perform normalization of the histogram; and a normalization unit normalizing any one of the histogram of the generated M blocks and the histogram of the corresponding M blocks in the past.