Said to be the earliest photograph of a UFO. The image is half of a stereo photograph, depicting a cloud formation over Mount Washington in the state of New Hampshire, with a cigar-shaped object. Photographed in the winter of 1870, and deposited with the US copyright office in 1871, and is in the public domain.
The original photo (at least, this is what the seller said it was) was auctioned on eBay in March 2002 and went for US$385. [Source: Wikipedia]