Adding Static Shadows

In a nutshell, I have a group of meshes for the landscape of a level. I also have a 512x1024 image for the shadows; white where there are no shadows, and black where there are. This image would, in theory, be applied top-down onto the entire (or certain parts of the) group of meshes and line up where the shadows are supposed to be in the landscape. How would I go about creating static shadows on the meshes with this image?