My understanding is that the physical 'image' in question was produced in the photo lab/department of the Daily Record (a Scottish newspaper) from negatives of which they were provided with from the alleged photographer.
The paper wished to have an opinion from the MoD on quite what the images purported to convey, and so the paper contacted the most local RAF press office (Pitreavie Castle in Dunfermline) and asked 'what do you think about these images we've been given?' and they said 'about what?'- send me a picture'. The paper then ran off a copy on an enlarger in-house (allegedly slightly out of focus) of the 'best of' a series of six negatives and sent it via mail to the RAF press office.
The press officer then, after looking at the supplied print, took some photocopies and faxed them to the MoD, asking what they should do. The MoD requested that the paper send the negatives to them, which the paper apprently did. The archival records suggest the negatives were returned to the paper, after their investigations, but they were apparently never seen again publicly.
The image has only come to light recently as no instruction was given to the press officer as to it's retention or otherwise (as copies had been faxed, then original negatives obatined) so those documents (image along with the original photocopies he'd generated in order to fax & the courier envelope) lingered in his office. The press officer took them home on his retirement some years later.
It appears that the physical image matches not only (unsurprisingly) the retained photocopies but also the low quality images (copies of the faxed photocopy) which are part of the documents available in the national archives now (in other words it's been a long con!).