Imagine that the only record of a key moment in a football game is a still photograph that seems to show a defensive back committing pass interference on a receiver. However, the referee didn't throw a flag on the play. Is it possible to be confident that the referee blew the call?
One reason not to put too much weight on the photograph is that anyone who regularly watches televised sports knows that different camera angles provide different information. A call that appears terrible on first viewing is often confirmed as correct when the play is seen from a different angle or a seemingly good call turns out to have been bad. A different angle might show much more space between the defender and the receiver than the photograph shows. It might show that the pass was in fact uncatchable. Moreover, a video might show that the receiver's motion and momentum were unimpeded despite the proximity of the defender so that he still had a fair opportunity to catch the pass.
It might help somewhat to get the opinion of football experts on the photograph, but probably not as much as one might like. The problem is that the photograph lacks the information that might provide greater certainty. No matter how many people agree that it appears to be pass interference, there is no way to be sure that they would reach the same conclusion if they saw the play from better angles.
What might be useful is to find similar photographs of plays where video is available from several angles. Then it would be possible to determine how frequently the impression given by the photograph is confirmed and how often it is contradicted. If it turns out that the referee's call is confirmed as often as it is undermined, then the best that could be said is that such photographs only raise the possibility that the referee erred. However, if it turns out that the referee's call was confirmed nine out of ten times, then such photographs would have to treated as providing little or no evidence of a missed call.
I am frequently asked by Christian apologists "How do you explain the experiences that led the apostles to believe that Jesus had been raised from the dead?" My usual response is "Why should I expect to explain them?" The evidence I have is simply not sufficient to give me any certainty about what really happened. I can think of any number of possible scenarios that, having been passed along an unknown number of times in an oral tradition, might have led to the stories found in the gospels.
The problem I have is similar to the one of the still photograph of the football play. The angle I have on the events doesn't contain the information I need to reach a conclusion. What I have is mostly the anonymous accounts of fantastic events based on unknown sources removed an unknown number of times from the original events. I only have a single first person account, but that account is vague and lacking in details. All of these accounts are written from the perspective of true believers in those fantastic events . What I would need to have any confidence in any conclusion about what happened would be sources closer to the events including sources with a skeptical perspective.
In fact, I have good reason to think that the kind of evidence I have is particularly unlikely to be accurate. Just as I might find photographs of similar football plays where video replays are available, I can find fantastic stories told by true believers years after the events where information closer to the events is available. I can compare the stories about aliens written in the 1980's to the primary source material concerning the events in Roswell in 1947. I can compare the stories that the Mormon Church tells today about its early years to the accounts that non-Mormons gave of their dealings with Joseph Smith. I can compare the stories that the nuns told me in the 1960's about the miracles witnessed by thousands at Fatima in 1917 to the much smaller number of vague and inconsistent accounts that were actually given at the time. I can observe that the fantastic accounts are invariably undermined when better information is examined and I can conclude that they are unreliable as evidence, just as I would conclude that the photograph was unreliable evidence if the video replay invariably confirmed the referee's call.
Of course comparing the New Testament accounts of the apostles' experiences to still photographs is far too generous to the former. They are more like stick figure drawings of the play by people who heard about it years later.