How to draw a Perspective-Correct Grid in 2D

Question

I have an application that defines a real world rectangle on top of an image/photograph, of course in 2D it may not be a rectangle because you are looking at it from an angl

Answer 1

In the special case when you look perpendicular to sides 1 and 3, you can divide those sides in equal parts. Then draw a diagonal, and draw parallels to side 1 through each intersection of the diagonal and the dividing lines drawn earlier.