From Art Geek:
I have been curious about how to make adjustments to paintings or drawings, by adding 3D objects which might otherwise be hard to invent and/or draw. The question boils down to how to 'composite’ 3D objects into a 2D scan or photo of an existing work.
It turns out the 'place photo’ option in SketchUp (Import… -> JPG or PNG / 'Use as matched photo’) works like a charm for this. (You can align the perspective of a given view in your model to that of your imported image, though that doesn’t really apply for this image.)
Once the 3D modeling is complete, just remove the background image and do an image transfer of the contents, or project or otherwise draw them directly on the painting. The new “Open” acrylics are a perfect match to this approach, since once can draw or transfer photos much more easily on top of acrylics than onto oils.