Clicking the Difference button 
performs a basic change detection algorithm by computing the difference between two raster or image service layers. This can be used to compare classified images, elevation models, and more.
This tool does not account for radiometric differences between images, such as atmospheric noise or haze. It also will not account for geographic shifts between two data layers. It only makes a pixel-over-pixel comparison. If the images are not perfectly aligned, this will show up as a difference between the images. Therefore, it is recommended that you preprocess the images to geographic and radiometrically shift them if required.
- To view the Image Analysis window, click Windows on the Main menu and click Image Analysis.
- Click two layers in the Image Analysis window.
- Click the Difference button .
The Arithmetic function is added to the temporary layer.
To improve the visible difference in the temporary raster layer, click the layer in the Image Analysis window and apply a different stretch or check DRA to display the layer using a dynamic range adjustment.