There are many ways to make tapestry crochet graphs from photos. The ideal subject is lit from the side and includes several values. A variety of graph papers and information about how to use them are included in my Tapestry Crochet and More Tapestry Crochet books. In summary, the image may be projected onto paper or placed under tapestry crochet graph paper on a light table. After tracing the major lines, the cells are then colored in with light, medium and dark colored pencils.
Another approach utilizes computer graphics. The below images were done in a just few minutes with Photoshop, but several other programs could have produced similar results. Reducing the colors of the photo helps visualize the crocheted version and often makes it easier to trace onto tapestry crochet graph paper.
The number of colors and the posterized colors themselves are easily changed in Photoshop.
The online site, KnitPro, quickly (and for free) transformed my photo into a square-ruled graph.
KnitPro just as easily produced the rectangle-ruled graph below.
To my knowledge, though, there is no computer program available that will fill in tapestry crochet graph paper automatically. Digital versions of the most popular tapestry crochet graph papers are posted in the files section of the Yahoo Tapestry Crochet group. The graph paper may be printed out, then placed over an image on a light table and filled in by hand or the graph may be digitally placed over a photo, then filled in (cell by cell) with the paint bucket tool.
For creating graphs of animals, flowers, etc., there are millions of free online images available for inspiration. For instance, Google “horse”, then click on “images” to find a profile view, then trace it onto the appropriate graph paper. This method helps achieve more accurate proportions and had I used one of those images, perhaps my horses would NOT have turned out like donkeys!