Why It Has Depth in It

A digital slid consists of a breadth of shots that are stereo pairs with each other. In other words, they suit the left eye and the right eye correspondingly. Thus, with a certain frequency of switching them, an effect can be achieved in which the eyes catch them and your brain interprets this image as in depth.

What also helps with this is having a background and a foreground around the object being captured, which intensifies the 3D effect.