The simplest explanation is that of gullibility. When a Christian hears a claim like this and accepts the story without question, rather than researching it to test its veracity, it's much easier to pass it along. Nothing underhanded or deceitful in that; just excitement that disengages one's drive to separate fact from fiction. If King's blog is to be believed, since he received many comments from those who didn't want to hear that they were fake photos, another reason could simply be desire. We want them to be true. Pictures like this could stand as a testimony to the authority of God's word, to lend validation to all believers who trust in the truth of God's word. National Geographic reports what the creator, IronKite, says about the reception of his work on this digitally created photo:
IronKite said he's tickled that the picture—which took only about an hour and a half to create—has generated so much Internet attention.
"I laugh myself silly when some guy claims to know someone who was there, or even goes so far as to claim that he or she was there when they found the skeleton and took the picture," IronKite said.
"Sometimes people seem so desperate to believe in something that they lie to themselves, or
exaggerate in order to make their own argument stronger."
IronKite brings up a very good point that believers should be wary of, namely that adding our lies to a proven forgery in order to strengthen an argument is foolish at best and downright sinful and destructive to our faith at worst (and in reality). The community of believers does no good to themselves or the Church of Jesus the Christ by latching on to fool-hardy stories before verification can be made. In a perfect world our faith wouldn't need validation. But this world is not perfect, so we do draw comfort from supposed proof.
Look at the doctored pictures closely. If they were ridiculously obvious forgeries, they wouldn't serve as digital masterpieces or as effective hoaxes. One shouldn't feel bad for not immediately questioning them at all. Rather, use them as the drive to later research similar claims before sending them along.
I have frequently said biblical scholarship should be approached less like a prison and more like a courtroom in the observance of this ideal: innocent until proven guilty. Or in our case, and in light of the archaeological discoveries unearthed using the Bible, true until proven otherwise. Sadly, many approach the biblical text as they would a walk through a maximum security prison: everything, and everyone, I see is dangerous and/or guilty until it can be proven absolutely and 100% true.
We should be lucky that no other area of any of our lives is placed under such inhospitable scrutiny.