Comparison by Scott Mardis of the Lake Champlain Mansi photo with a Plesiosaur skeleton and with a carved horn artifact from Vermont of the Colonial age. This also looks like a very firm connection.
Jay Cooney has also just published Scott's article on the Mansi photo on the Bizzare Zoology blog:
http://www.bizarrezoology.blogspot.com/2014/04/blog-on-an-analysis-of-mansi-photograph.html