Someone from the AUGI website suggested making a mass and applying the required image as a material. This entails lots of mucking about, but it does work. Your image needs to sized to the same length as the mass or it will tile, and the mass needs to have the same proportions as the photo (usually 6:4.5 for a digital photo, or 6:4 for a scanned photo) in elevation or it will tile. Also, as the mass is usually drawn in plan view it will rotate the image to the direction of the extrusion, so you will need to rotate the image 270deg when setting the material properties if you draw it in plan.
I, too, would be interested in knowing how to add image files to the presets available. I tried dropping extra images into the presets folder, but as GL notes, there is a bit more to it...
Autodesk needs to include the option for a different background with the presets - after all part of the reason for all this modelling is presentation and while we can model the immediate background, it is very stupid to think we will also model the distant background. Clients often want to see their product in the correct context and at present we can't do that for them without a lot of mucking about! We could do it in ArchiCAD and I remember doing it 10 years ago at university with 3Dstudio viz - so why not modern Revit???