`ImageDifference[a, b]` gives the absolute difference of two images of the
ImageDifference[image1, image2]
ImageData[ImageDifference[Image[{{0., 1.}}], Image[{{1., 0.}}]]]
→ {{1., 1.}}ImageData[ImageDifference[Image[{{0.1, 0.7}}], Image[{{0.3, 0.2}}]]]
→ {{0.20000001788139343, 0.5}}ImageDifference[Image[{{0., 1.}}], Image[{{1., 0.}, {0., 1.}}]]
→
ImageDifference::imginvd: Expecting images of the same size in the input.
ImageDifference[-Image-, -Image-]