Using the Polygonal Lasso Tool, create a triangular shape.
Cut the piece out (Cmd/Ctrl + X) and create a new layer. Paste your selection onto a new layer.
Use the Gaussian Blur filter (Filter > Blur > Gaussian Blur), setting the radius to five pixels. Repeat this several times with different selections from the layer below, to give the illusion of depth – objects that are blurred often seem closer to the viewer.
Repeat Steps 08-10 about ten more times. To add depth to the image, try a variety of shapes – here I’ve used rectangular shapes as well. Be creative in your selections using the Polygonal Lasso.