Glamour photography has several goals. The primary goal is of course to draw the interest of the viewer, in order to keep the viewer looking at the image. Further, we strive to direct the viewer's attention to the areas of the image we want the viewer to look at, and in the order we determine. Even better, we would like the viewer to want to be in the scene with the model.
When doing glamour composites, this can be a real challenge, especially when we employ high dynamic range (HDR) backgrounds with saturated colors. The viewer instinctively knows such a scene is not real. Realism declines further when elements that would not normally be in the scene are added. Here is such a glamour composite, featuring the lovely Andrelica. The background was taken in an alley of the Arab Street district of Singapore. To make it yet more surreal, water was added in the post processing. Look at the image, and see if you can determine what problem was avoided:
If your answer is that the vertical lines of the background are vertical, and the horizontal lines are horizontal, you are completely correct. This scene was photographed with a perspective control (tilt-shift) lens, with the camera perfectly vertical. If you are inside, tilt your head every which way. Notice that the horizontal lines of the room stay horizontal and the vertical lines stay vertical. Your brain makes the adjustment that a camera cannot make. Consider this unretouched image of Andrelica:
This image looks like a photograph taken with a tilted camera because the horizontal and vertical lines are not true. The viewer knows he or she is looking at a photograph. I prefer to give the viewer the impression that he or she is looking through a portal into another world - not looking at a photograph. Here is the same image, retouched, with some cropping and perspective control applied, using Lightroom's crop tool:
The viewer will only give us so much leeway, so we can stray from realism only so far. Keeping the perspective correct at least gives us a chance to make the viewer wish he or she was there, in the scene, with the model. The best way to do this is to keep the camera vertical. If this cannot be done, then use Photoshop to Transform -> Skew.