The image viewer support 2 types of overlays that can be useful when prducing imagery for publications.
Zoomboxes can be added via Overlays->Add Zoombox. The placement area of the zoombox can then be selected by clicking on two distinct texels of the image. Afterwards, a dialog will pop up in which you can select the color and border size of the Zoombox. In the following example, the blue box was added:
During export (File->Export), the contents inside these zoomboxes can be exported as well via the dialog. Make sure to check the Export Zoom Boxes checkbox in the second export dialog. The scale parameter allows you to upscale the contents inside the Zoombox via nearest neighbor upscaling:
The arrow overlays can be acessed via Overlays->Add Arrow. Place the arrow origin by left clicking any texel in the image. Place the arrowhead by left clicking again. The thickness of the arrow can be changed with the + and - keys after the first left click:
The arrows will be included when using File->Export.