There are really two parts.
1. Highlighting an area/element. There are a variety of ways to draw to the page view to indicate highlighting. Be sure to test un-highlighting!
2. Selecting an element. Requires that you iterate over all elements, deciding if a mouse click applies to it. Consider whether you want to implement overlapped selection, and how you want it to happen.
You will need full and detailed understanding of the graphical image model from 32000-1; the API alone will not give you enough information.