Preview is a great application for vieweing images or PDF files. My co-workers who new to mac complained that they can not open multiple images in one window like in Windows image viewer. They did not know that Preview is able to do so, it just not by default. To make it work, open Preview Preferences or just press CMD + , and than follow this preference below.
Close the Preference window, and try to drag more than one image to Preview, just like this.
