How to print textures on objects in runtime?

I am searching for an more or less easy way to print textures on objects in realtime. For example I want players to leave footprints, so I want a normalmap printed at the footposition. Or I want cars to leave tracks.
What are methods to do such effects in Unity?

you can change a texture of an object like this:

        public Texture2D tex;
        			tex=new Texture2D(2,2);

 // if you really really want to draw on an actuall texture you can set the color of pixels like this:

           tex.SetPixel(1, 1,;


but if you wanted footprints you wouldn’t change a texture, you would create a separate footprint object and simply spawn it on top of the terrain.
You would use a simple plane object with a transparent shader.

Thanks. I was looking for the second way to do it. Can I only have an normal map applied with this transparent shader or do I need to give the footprint also a diffuse tex?