(This question is coming from geospatial background and not a 3D modeling background, so I may have some terms mixed up)
I am using the BlenderGIS add-in ( https://github.com/domlysz/BlenderGIS ) to easily add geospatial data to Blender. Primarily I am using it to combine elevation and aerial photos to create scenes similar to what you see in Google Earth. The aerial imagery is "draped" onto the surface. Basically a pixel of the 2D imagery is shown on the 3D point of the 3D surface, from a straight down perspective. This results in photorealistic view of the terrain at "airplane window" scales. The technique works great except for areas with extreme topography such as sheer cliffs. With cliffs, the result is unnatural streaks.
To counter this I would like to figure out how to "drape" a surface photo onto the side of the surface, and then blend it with with the top-down aerial photo. I'm fine with breaking up a photo into reasonable parts to get it done. I just need to know how to designate the area that each photo part should be "draped" to the surface.