Caravaggio Cheated

well, not really, he just did what many artists have done throughout history
Caravaggio used 'photography' to create dramatic masterpieces.

Amor Vincit Omnia by Caravaggio

There are many purists/art snobs who claim that the use of projector or a photograph is cheating and will dismiss the work of an artist who does use them. The interesting problem with that view is that they will have to dismiss a whole slew of artists in history whose painting and drawing skills are unquestioned. One can't just copy a photograph/use a projector and render a realistic painting without a solid background in drawing, and anatomy/life drawing.
Vermeer and the Camera Obscura

Famous Painters who copied photographs.


Using photographs for reference
I knew that I wanted this painting to have a formal studio portrait effect so I took this photograph of my daughter as a reference. I wasn't trying to make an exact likeness, but capture elements of several women in my life, past & present and women who have inspired me.

There dances the shadows of women past and present
Their voices humming softly
I hear them

So next time someone gives you a hard time about using photographs or a projector (camera obscura) tell them if it was good enough for Caravaggio, Canaletto, Vermeer, Sir Joshua Reynolds it's good enough for you.

Advice
Better to use your own photographs (or with permission of the photographer) unless you want to get in a pickle like Sheperd Fairey
From the view of a photographer on the use of their images please check out
Visual Perspective on the issue of copyright.