This is not really a Warhol, but maybe it helps me for my 15 minutes of fame. For your 15 minutes of fame there is the free online tool BeFunky.
BeFunky is a post-processing tool for photos or other images you can upload from your hard disk or via URL from the Web.
It has no filters to enhance the brilliance, like Photoshop Express, but allows you to transform the photo in a certain art style. So, you can transform it into a sketch, a cartoon or even into Warhol popart.
It is pretty easy to use and has a lot of extra features to add to your transformation, like frames, bubbles, text or accessories. Within 5 minutes you can create something like the image in this post, that is based on the image you can found in the footer of this blog. It makes a lot of fun to work with BeFunky.