I am vertex painting using Cycles, & I have set up nodes to plug the vertex colors into a shader & it paints on & works fine, renders etc, looks as expected. But vertex painting gives a brush color choice only - Question - is it possible to use an image bitmap instead of the brush colors? Or - is vertex painting only for colors? I made a material with an image, unwrapped my object's surface, but so far I can't find a way to use this image as the color source (apart from just putting this material onto the selected surface area).
Under the brush settings, in Texture, click New. In the properties panel, in Texture/Image click Open, then locate your picture file. You can now use the picture as a brush.