I never work from a single photo when drawing a celebrity portrait. I feel like that would be stealing from the photographer who took the picture. Also, I can rarely find the exact lighting, facial expression, and angle I want in a single photo, so I combine elements from a group - and then make up the rest.
Case in point, Mads Mikkelsen as Hannibal Lecter.
If necessary, I'll also use some reference photos of myself, as I did here holding the dish.
The Hannibal steak was drawn by closely watching the Visible Human Project's videos of thinly sliced cadavers.
With all of the pencil work finished (except for the sprig of parsley, which I did last), I moved on to the plaid/tartan suit pattern and shape, all of which was done in ink using a brush, a Pilot Parallel pen, and wooden strips to make various marks on paper.
Then everything was assembled and colored in Photoshop.
I received several comments online about this resembling a "South Park Canadian" which I had to look up because I don't watch South Park. There would have been a fascinating synchronicity to this if Hannibal were Canadian, but he isn't and neither are any of the actors who've played him.