How to load Paint Texture dynamically ?

i mean that the paint texture is not pre-loaded or pre-decribed in the material file,
when i want, i can select a image file from local folder,
then it will be added as the paint texture,
perfectlly , the texture can be added with no limmit.

how to do ?

i find a article here:
viewtopic.php?f=16&t=8989

let me try it first.....