Let's say you have a scene in which there is a hot air balloon rising well above the ground and your goal is to place a person in this scene. How do we need to shoot that person for maximum integration? What we need to consider is what angle the camera was pointed at when capturing the photo of the balloon. Obviously, we can see the underside of the basket of the balloon... to some extent, right? Why? Well, because it's above the viewer so the underside is visible. That tells us that the camera was pointed up. Though we don't have the luxury of always knowing what the exact angle was (especially if we're using stock photos), optics and lens distortion always leave clues...
Ever notice how when looking up at sky scrapers the bottom is wide and the top is narrow and tiny? We don't even need to know why... we just need to take note that this is what happens to objects when we view it through the viewfinder while pointing the camera up. Soooo, what are we going to do when we take a photo of the person for our scene? You guessed it, we're going to point it up. How much? Experimentation and observation is the key to know how much, but once you nail it, the blend is perfect. What happens if you don't observe and respect this principle when shoot/creating your works of art? Well, if the building is offset as it is when we point the camera up (the building looks like it's falling over backwards, doesn't it?) but the person is shot with the camera pointed level? The person will look like they're falling forward... not exactly the effect we're going for.
Here's a quick composite I made to illustrate perspective using a couple of stock images and our trusty LayerCake Studio Magic panels:
Notice how we can see the underside of the chin, shoes, nose etc. This is consistent with looking up at the building. He's bigger at the bottom and smaller at the top, just like the building is.
Another aspect of perspective isn't just angle. We also have height. Let's say we're not pointing our camera up OR down. We still have to decide the camera height from the ground. We could shoot the model at eye level or down by the floor. Again, which do we do? Look at the scene for clues. If there are cars in the scene, can we see the tops of the roofs or are we eye level with the headlights?
I purposely used an extreme angle and example today to make a point... that it DOES matter what angle and height we shoot from when trying to integrate our scenes with our elements. Hopefully you've become sensitized to perspective and height and will be able to decipher what your scenes are telling you about how to shoot the elements.
Up next: Compositing rule #3: Size & Scale (correct proportions). We'll talk about what kinds of observations to make to decode this mystery! Till then, keep that camera pointed in the right direction and at the right height. Happy compositing!