Use the ASCII Artist at http://www.glassgiant.com/misc_ascii.php
Upload image, e.g.
In this case the image is 126 pixels wide by 159 pixels tall. A latchhook is basically a bitmap image with 4 dots per inch (DPI), so the resulting latchook in this case would be 31.5" by 39.75".
Get output; there should be 3 characters.
I ran a Find in Homesite+ and got the color breakdown:
You now all the data you need to make your very own gigantic latchhook of Che Guevara. Expect to work a long time putting it together, though. I would estimate 40 hours.