Stereogram 3D is tool for drawing stereogram using your iPhone. It has features for using an depth map* to create a random dot stereogram. You can start with samples. Also you can draw your own shapes on the black canvas and create a graphical stereogram with the hidden picture that you have drawn. If you already had a depth map image in the picture library, you can just load it and make the stereogram directly.
*depth map: Usually, the depth map is a gray-scale picture, with lighter shades representing less depth, and darker shades representing more depth.