From the American Society of Media Photographers’ interview with Jill Greenberg:
ASMP: Your photographic style has been widely imitated and your images have been subject to unauthorized use. Please offer your insight into how to address and resolve either or both of these issues.
JG: I am still figuring this out. It’s not possible to trademark a lighting approach, despite being (at the very least) widely acknowledged as the originator. In the fashion and tech industries there is something called Trade Dress, and I honestly think this could and should be applied to the visual arts as well, but I do see the difficulty in that.