However, there is a difference between taking a brightly lit underwear model and transforming him into a moody Batman on a rooftop overlooking the city and copying someone else's artistic expression.  (One can argue that the underwear model was still posed and lit by the catalog photographer in his own artistic way, but that argument only goes so far.)  I have to agree with Peter Martin above--too many of the artistic choices in the painting were chosen by the photographer.

If I copy a car in the background of a newspaper photo about a building on fire, that's different than exactly copying an Ansel Adams or Annie Leibovitz photo with all their lighting and framing, etc.

Why are Batman's gray thighs darker than his gray arms and torso?  Only because the photo guy's thighs were wearing black pants, probably.

I give credit to anybody who can paint realistically and copy so exactly (whether he traced it to begin with or not--if tracing were that easy to pull off successfully, EVERYBODY would do it), but sometimes being LESS exact is actually better.

Swipe-using another artists work (whole or part) intentionally but used as though the work was their own.

Homage-using another artists work (whole or part) intentionally but with the audiences understanding that it originated with another artists. 

Photo Ref- Er...using a photo to refer to during the process of producing art.

The issue with photo-ref-ing is to what extend do you use it. To figure out the pose, where the hair line should go at the tilt of the head, lighting, texture et al. Or just trace the whole thing!

Any tool that becomes a crutch is no longer a tool but a handicap.

-D 

This obviously isn't just a case of using a photo for reference, it's depending on it for a large chunk of the creative process.  I wouldn't be surprised if there's a photo that was copies in order to add the skyline as well.

Darren - I would describe an homage as a piece of art inspired by an existing piece and done in a way that doesn't try to hide that connection.  In comics most of these are easily identified, whether it's a nod to Fantastic Four #1, Amazing Fantasy #15, Giant-Size X-Men #1 or some other well-known work.

Pop artist Roy Lichtenstein swiped.  Comic artist Greg Land swipes.  Wally Wood had a famous quote about it - "Never draw what you can copy, never copy what you can trace, never trace what you can cut out and paste up."  So it's a long-used method.

I love photorealism, but I love art more. There are a handful of artists whose art I adore that isn't really quite a "slice of life" - but I'm purchasing a book for entertainment, not instruction.

Were I an artist and I would find the perfect pose for Captain Fonebone, I believe I would have it on my table as a reference... but I wouldn't copy it line for line. If naught else, that's not what I'm being paid for.

Bottom line: if Mr. Adams asks, "Are you drawing professionally?", my answer is, "No, and that's not the point. I'm PAYING his 'getting paid well' salary, and if he wants to keep getting my money, he won't do things that aren't acceptable to me.

Your answer seems to be: tracing is OK, so therefore it's reference. 

In which case, what is a swipe?

By the way, the photo doesn't come from a photo reference book, it comes from the wonderful world of microstock photography. (here, in fact: LINK)