It Takes Two to Research Tango Photos

Dear Rich: I need to identify the copyright owner(s) of a collection of photos related to the Argentinian dance tango. The intention is to use those photos –- mostly if not all of them -- in Argentina, in a book of mine. Can you suggest a commercial service which could help?
Many professional photo researchers (like Laura Wyss) belong to the American Society of Picture Professionals and you should be able to obtain a referral from that organization. Alternatively, you may have better luck obtaining international rights by using a photo researcher affiliated with the British-based Picture Research Association.