Thats the big question — who can authenticate a lookalike for a famous person?
In general you need some provenance or supporting documentation. Not too many people are willing to stick their neck (or their wallet) out based upon a resemblance. I would start with the National Portrait Gallery in DC and any illustrated books on the person. See if you can find other daguerreotypes of him or, even better yet, an engraving that might have been made from YOUR daguerreotype or a least at the same sitting (judged by the clothing, backdrop, etc.) Sometimes things do fall into place.
