Find three equal pictures with a clear 3D layout (what is in front and what is in the back). Cut out the figures to become this:
Pic 1: The complete picture for the background
Pic 3: Details which will come on the foreground
Pic 2: The in-between layer
Fixate pic 1 on the card with (preferably) a photo glue.
Use a small sharp tool (e.g. a wooden stick) to randomly place small dots of 3D-kit or silicone kit on the backside of picture 2. Try to make them all in the same size!
Use a pair of tweezers to place picture 2 on picture 1. Take care of a proper alignment. Gently push on pic 2 to make all heights equal, 1-1,5mm will do nicely.
Let this dry for some time.
Put dots of kit on the back of the top pictures and stick them on picture 2. Take care of alignment and distances.
The dots under the pictures create an extra sense of depth.

Instead of kit you can also use 3D-tape or another tape with a proper thickness. In this way the distance from layer to layer is always the same.
Variations: Leafs of a plant looks nice if the kit does not have the same thickness everywere. You can also manipulate the paper a little bit to make it speherical instead of flat.