Image Map Regions
Image Map Regions are used to create transparent areas over images (or any place in the wireframe) and allow for adding Annotations and Interactions to sections of an image. This is particularly used after importing screenshots of an existing system or from other tools.
A mask is available for Image Map Regions so they can be seen while designing the wireframe. The mask can be show or hidden by clicking Wireframe->Mask Image Map Regions in the main menu.