If you look closely, you'll see that the image is surrounded by a blue rectangle with a bunch of little white squares on it. This blue rectangle is the objects bounding box.
The bounding box appears whenever an object is selected. It shows you the actual size and position of the object. (As you can see, when you add a new image object, it gets selected for you automatically.)
Note: The bounding box is only visible at design time, when you're working on the project.