Said to be the earliest photograph of a UFO, but is in reality a heavily-cropped portion of a stereograph. The original stereograph depicts frost formations on rock (not clouds as say <a rel="nofollow" class="external text" href="http://lt01.nypl.org:9001/StyleServer/calcrgn?cat=NYPL&amp;item=/5-31-2006/g91f031_006fd.sid&amp;wid=420&amp;hei=400&amp;plugin=false&amp;style=default/view.xsl&amp;browser=win_ns6">here</a>]).  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.
User <a href="https://en.wikipedia.org/wiki/User:Tempshill" class="extiw" title="en:User:Tempshill">Tempshill</a> on <a class="external text" href="https://en.wikipedia.org">en.wikipedia</a>
Winter 1870 <div style="display: none;">date QS:P,+1870-00-00T00:00:00Z/9,P4241,Q40720553</div>–1871
<a rel="nofollow" class="external free" href="http://www.ufoevidence.org/photographs/section/oldest/Photo134.htm">http://www.ufoevidence.org/photographs/section/oldest/Photo134.htm</a>