Find the differences games are classical games which are based on observation and comparison. In general you have 2 images that look identical at first glance but where some details are in fact different. And it is precisely these details that you need to locate on a few glances.
Some games have a storyline (eg Moonlight Difference or Music Box of Life), which gives even more eager to find the differences between the images! Indices are also available in order to advance when you really do not know and you are blocked.