So, with a bit of fiddling, I photo-shopped the image and enhanced the lines a little to get this image:
Then it was a question of cropping this and doing more Photo Shop trickery to try and turn it into an image that would look good on a tile.
I turned it into a simple black & white line drawing, shrunk it right down and then added blended chalks in pinky/purple to give it a bit of a coloured background.
Here's how it ended up (although it still needs another coat of glaze and a hanging bail).
The photo is not brilliant as it's so hard to see pale colours as the glaze is so reflective - it does look better in real life, I promise!