Here’s the 26-step tutorial which describes how to… turn somebody into stone. The GIMP will be needed, and an image that shows a person that you want to turn into stone.
It is a very very hard thing to turn people to stone and make it look real. Not every picture can be used and there is a lot of fine-tuning necessary. If the effect is not working well just give it a new title: “Turning people into a zombie” 
