I agree on this, there is some old photographs that have a lot more potential than the vast majority of the recent ones to be real UFO (not aliens but UFO)
The one you posted is the most known of it's kind, Robert Sheaffer document pretty much proves that the photo can be a fake although it's doesn't really prove that is not genuine either. I'll quote some interesting points of it.
Another interesting,large and awfully detailed analysis of the photo can be found here http://brumac.8k.com/trent2.html
In my opinion the photo is hoax judging from how stationary the disk looks it looks as well as from the size of it.
To accept that if a photo cannot yet be proven wrong then it must show something real and especially an alien flying cab it requires a bring big leap of faith.
The Cottingley Fairies lasted as genuine for over 70 years and they were just cardboard.
That doesn't mean that in 1920 the correct answer to the question "Does fairies exists?" was "Yes, take look at Cottingley Fairies photos that seems genuine"
Some photos are unexplainable yes, but the UFO in them is an "unexplained object" not an "explained by aliens" object, that's the bottom line.
Edited by Keosen, 27 July 2011 - 08:45 AM.