1. A method for automating validation of appearances of graphical user interfaces, the method comprising: creating proper-display metadata defining an appearance of a user interface of an application as it is supposed to be displayed on display devices of users using the application; performing a test run of the application; during the test run, capturing a set of image(s) which capture how the application actually displays on a test display device of a test user; converting the set of image(s) into test-run metadata defining an appearance of the user interface of the application as it is actually displayed on the test display device of the test user; comparing the proper-display metadata and test-run metadata to determine that the test-run metadata and the proper-display metadata are different; responsive to the determination that the proper-display metadata and the test-run metadata are different, saving the set of image(s); further responsive to the determination that the proper-display metadata and the test-run metadata are different, assessing, by a tester, the saved set of image(s) to determine whether the test run reflects a problem with the user interface of the application.