Oh ok.
I use a depthmap. It's a black and white drawing on which the black is the background of the image you want to convert and white is the foreground. Then you have all the nuances of grey between the black and white for the other levels. I use GIMP, a photoshop-like software to draw the depthmap. I open the original pic with GIMP and I open a new layer for the depthmap. With some transparencies, I can use the original pic as a guide while drawing the depthmap. Once the depthmap finished, I save it as a jpeg format and I use another software, Bas-Relief, for the conversion. I load the original pic and the depthmap and then I have a 3d pic. I have put a lot of depthmaps on my gallery in a folder called "depthmaps". There is also a group called "depthmaps" here on deviantart. I have also done some tutorials with screen captures, you will find the links on my journal but my tutos are written in French. There are also a lot of tutorials on the internet. Just remember this, the depthmap is the more important step for a 3D conversion.