The LaTeX Overlay Generator is a great tool to annotate images which contain sub-images like this (where the sub-images are all rectangles and all "horizontal with the screen"):
However, some images contain sub-images in the following manner (where they are not all "horizontal with the screen" and rectangles may be chopped off):
The LaTeX Overlay Generator unfortunately is not able to rotate rectangles (I have tried to do it afterwards, but not in an easy manner), and even if it could, one would still need to find a way to "chop off" the whole image afterwards.
Perhaps there is another handy way with Tex then? For inspiration, cf. Drawing on an image with TikZ. Or perhaps there is a GUI to make it happen?
P.S.: I have added a green border on top of the polygons (all chopped-off rectangles), since that's a functionality of the LaTeX Overlay Generator which I would like to preserve/mimic.
P.S.: I would also like to have text (annotations) inside the sub-images, in a later stage.