The PLUS Coalition is a not-for-profit collective supported by associations and companies representing professional image makers to assist rights management. They have launched a beta of the PLUS Registry that connects image makers to image buyers through metadata. Photographers can join PLUS Registry free to register their details so photo buyers can locate you.
With Orphan Works bills in the USA, Europe and Australia under consideration it is essential photographers make it simple for potential photo buyers to find you: or they could legally use your images for free.