Documentation - Image Compare
To get image comparison window select menu [Window -> Compare Image] or simply click on "Compare" button in tabs window in the bottom. This will open auxiliary image view in the right side of the image window. Both images are separated by comparison tool buttons. In the default state all movements and zooming from the main window are reflected in auxiliary window automatically.
 Open Image To Compare - Shows browse file dialog to open image to be compared. You can also easily copy the image from the left side pressing button .
 Track base image movements - If this button is pressed the right side image repeats all scrolling and zoom operations done on the left side (base) image.
 Copy image left to right - Copy the image from the left side to the right.
 Copy image right to left - Copy the image from the right side to the left.
 Swap left and right - Swap images between sides.