Let's take a look at why photo miniaturization works and how to perform it digitally, off-camera.
It is important to note that when we speak of miniaturization, we do not refer to what is known as Tilt-Shift Photography. Such photography requires expensive, specialized equipment and is rather restrictive. We’re actually referring to “Digital Miniature Faking”, a method with greater flexibility than it's analog cousin.
How does it work?
Simple: when we miniaturize, we falsify a plane of focus (POF) onto the photograph's subject and apply an unnaturally shallow depth of field (DOF). This tricks the mind into thinking that our subject is much, much smaller than it actually is.
This is the original photograph, shot at f/7.1 - 1/500s. You’ll notice that most of the photo is in focus, or in Tilt-Shift terminology, the photo has a deep DOF. This is illustrated in the next photo.
The green represents our focus. The red portions fall outside of the DOF and are therefore out of focus. Note that the building’s focus doesn't gradually fall into red like the rest of the shot. Why? Because it’s a giant, vertical structure that doesn't follow the geography of the rest of the shot. The entire building, from top to bottom, is (for our purposes) an equal distance from the camera and fully within the photo's DOF. This is the key to understanding how Tilt-Shift editing works. Again, because this is your take-away fact:
Here's what happens when the building's focus is not treated independently with that of the surrounding landscape:
You'll notice that the top portions of the building's focus fall off along with the rest of the photo. This does not trick the mind into thinking the subject is a miniature. This looks like an oddly-stylized focus technique (which, incidentally, is what a tilt-shift lens would achieve).
Okay, so what would the focus look like on a properly miniaturized photo?
Here we have successfully truncated the photo's focus into a proper miniaturization. The final product is that of a subject in the center of the plane of focus, just barely fitting into the artificially shallow depth of field. This produces a photo that appears to be shot from a very close distance with a wide-open aperture, which is virtually synonymous with macro photography.
"Oh, what an adorably tiny building!"