Hi Sorry it's taken so long to get back, ok.... It's dead simple I just scan in a regular pencil sketch which was done on white Bristol board. Then add a background texture in photoshop, add a few highlights with a soft brush.
Hope this answers your question and thanks for the interest, appreciate it!
this is absolutely beautiful!! would u give me the rights to tattoo this on my friend? i am a licensed(professional) tattoo artist.... i will send you an image of the finished piece if i ever get to do it!