H, I have what I hope will be a simple problem to resolve. 

I'm creating a 3d environment using photographic images to texture the geometry, so it's basically a very elaborate camera projection map/matte/composite scene. Not sure of the exact terminology.
I have a model of a shed that I have succesfully lined up, and projected onto, my main photographic image using a perspective projection based on the camera with an image plane. 
That's all pretty much fine, but I want to texture a side of the shed with another photograph that I have taken of the actual shed in question, but I'm having trouble with getting the textures to display correctly.

I'm using a layered texture node and have set up two UV maps of the object (map1 & uvset1) which both contain UVs of the entire geometry. I assigned the image of the side of the shed, which has an alpha channel making all of the photograph surrounding the side of the shed transparent. I UV linked using the relationship editor. Then assigned it, I think through a lambert.

What I'm getting is not the desired result, and I can't tell exactly what adjustment I need to make.

Also, the images aren't displaying the UV editor, it's just grey, so I can't try to fit the UV's over the alpha properly.

I can't really find any tutorials that address this particular method. But any help understanding what I'm doing will be fantastic.

Many thanks for any response