http://www.renderosity.com/mod/gallery/index.php?image_id=1941805&user_id=343328&np&np

Flames can be placed on flat planes with a point light behind it to shed light on a scene for a still image.  You need a good image and a well done mask to isolate the flame.  But the question remains, as SoulTaker posted, will it be for still or video images?  Someone else may suggest ambient lighting from a flame model, but I don't believe you can get a realistic flame illumination.