Hello, I am going to have a stab at this for ya. When dealing with objects in 2 dimensions, we need to deal with perspective. Remeber that when you're taking an image, you're mapping a 3D space into a 2D plane, that's how we can tell if things are far away in an image. Same trickery they use in Lord of the Rings to make Hobbits.
What I am getting at here is we need to change the shape of the squares on an image to indicate the distance of them from the perspective we're looking at. We know that they're squares, but if you measure them in the image, they're actually non square, they need to be stretched or shrunk to appear further away. So when transforming from a non 90 degree angle, you need to transform them from a general quadrilateral into a square. I hope this makes sense, and I've uploaded and image of 3d street art to help illustrate this effect.
This image has two different resolutions has well, due to the way we map 3D objects in a 2D space.
