These images by Martín De Pasquale are so surreal that, obviously, you know they aren't actual photos. But they are perfectly executed. And the reason for that is not awesome Photoshop skills as much as good planning. If you want to make perfect photo composites, it's not that hard if you plan in advance. Martín's examples will show you how to do it.
Matching the color and lighting of all the elements of a composite image is the most difficult part of the process, so the key to be successful (and quick) is to shoot the individual elements in the same setting, with the same lighting.
In this case, you can see the base image—Martín playing with an incomplete drum set—and then different batteries in different positions, taken closer to the camera so they are easy to composite later.
Another one playing with scale. I wish giant dogs like these existed.
And here are all the elements, photographed at different distances to ease the composite process.
More scale fun. This time Martín is the giant.
And again three shots is all that's needed for that final image. The lighting makes it all look believable.
Multiplication is also easy.
You just need as many photos as you want to multiply any object, without moving the camera.
Here's another smart one which is easy to do: playing with body parts.
This one is a bit more difficult, as it requires some illustration to simulate the severed neck in addition to the planning to simulate the floating body.
You can also composite several people in the same photo, even if you move the camera.
You just need to hit the right angles and positions. In this case, a bit of blurring was needed to simulate the motion, but it's nothing complicated.
This one is great: combining tilt-shift photography and close up photography to further accentuate the illusion of photographing a model.
This time Martín didn't use the same matching technique as previous photos, opting for an straight forward black background for the hand.
Here, the box is not real...
...but a simple illustration. Having the subject pose inside an object with the same physical constrains as the simulated object (the box), is what makes it look realistic. This technique is good to keep in mind if you want to compose any imaginary object that requires interaction with the physical world.