There have been several times when I’ve needed to combine a photo taken at one angle, with a photograph taken from a slightly different angle.  The complexity of coming up with an acceptable end result increases with the differences between the angles of both pictures, as well as the lighting (and the resulting shadow incompatibilities.)  In this example, we’re going to take a stained glass window from a cathedral’s interior, and integrate it into the exterior of a different cathedral.

The first step will be to copy our target window onto the canvas of our destination cathedral.  I’m going to reduce the opacity of this layer for awhile as I work with it, to aid me properly placing and transforming it (right click on the layer, chose Blending Options, and then reduce the Opacity slider.)

The first tool I am going to use is the Edit > Transform > Scale tool, in order to get it close to the correct size.  I’m going to err on the side of keeping it larger, because when I resize this layer, I can’t increase it’s size without reducing it’s quality.

Next, I am going to use the Edit > Transform > Prospective tool in order to fix the angle incompatibilities between these pictures.

Now I’ve got to get rid of all the black that surrounds the window.  I used the Quick Selection Tool (this is a new tool in CS3.  If you’re using CS2 or below, the Magic Wand should work fine for you) to select the black and delete it.  I’ll also delete everything below the ledge.

The next issue to confront is the top of the arch, which is quite different than the shape of our window.  I’ll use the Edit > Transform > Warp tool to drag the top of our window up to to simulate this shape.

To wrap things up, I’m going to delete parts of our window where the underlying image should appear to be above it.  To add a 3 dimensional look, I’m going to add an Inner Shadow to our window.  Also, we need to make the window black and white to match our target image.  We can quickly accomplish that by hitting Shift+Control+U

This gives us our final image, and to the untrained eye they will have no idea that the window they’re looking at belongs in a cathedral thousands of miles away.