You don't apply materials to an image (which is a texture itself). And the side wall textures are part the Match Photo image, they aren't a separate texture. What you might do is create a new material that looks like them and apply that to the faces in the model. In GIMP I have sampled, warped part of a Match Photo texture and applied that as a tiled texture in a model (don't tell anyone). But you might just start with a new wall material and adjust it to match the color and texture in the photo.
In your Match Photo scene, Use the Style window, and edit the style. Go to the "Modeling" tab (last blue one) and turn off the foreground photo under "Match Photo". That will show you the materials you've applied to the faces while in the Match Photo scene. If you want to project the photo onto the model faces, Dave has done that, I think.