The Visual Annotator is an APS feature, which allows you to created rectangular clipping from images and include them as part of a document.
One example of use for the Visual Annotator are the pictures of the exhibition halls in the GDK Research project (see screenshot). In these historic pictures, individual works of art have been marked and documented as separate objects.
The people working on GDK Research also marked the doors between the halls, thus creating a virtual exhibition. This has been achieved on a rather tight budget. The user is able to navigate the exhibition not only chronologically and by topic, but also room-by-room.