ImageDifference

ImageDifference[image1, image2] gives an image where each pixel is the absolute difference of the corresponding pixels in image1 and image2.

Examples

Compute difference between images:

img1 = ExampleData[{"TestImage", "Lena"}];
img2 = GaussianFilter[img1, 5];
ImageDifference[img1, img2]

Detect changes:

ImageDifference[img1, ColorNegate[img1]]

Please visit the official Wolfram Language Reference for more details.