I know what you mean.
Here's a site that shows the twisted pyramid as well as the traditional pyramid illusion:
http://nataliewallacecards.blogspot....id%20Decoupage
I've attached a Reversed Pyramid Illusion picture. I don't remember where I got it, but probably from Circleofcrafters.com.
The way to do the tradtional version is to make 5 or 6 copies of a picture. You'll use one as the base (bottom), then, remove 1/4" from all sides of one picture. Remove 1/2" from all sides of another picture. Remove 3/4" from all sides of another, and so on. Then using double sided foam tape (if you don't mind it showing from the sides or Zots (or other clear adhesive dots) if you do mind them showing), place along the near the edges on the back of the pictures. Place the 1/4" removed picture on top of the base (uncut) picture. Then place the 1/2" removed on top of that one, and so on.
For the reverse pyramid, you do the same, except from the
center of the pictures instead of the edges.
I'd love to know how to do the twisted pyramid illusion.
HTH.
Joan