There is a site that will transfer a picture to a graph, but it doesn't always turn out well in my experience.
I just made some charts, and what I did worked out beautifully.
I printed out some knitter's graph paper, and then used that paper to copy the picture I wanted to knit onto the graph. This is a good site to get paper to your gauge.
I've also copied graph paper onto a transparency and put it right over the picture.