Bob, Agreed, its a bad quality picture however, the picture in post 73 in its current resolution is good enough for me to see the strap.
I think if you increased the ppi you may have only added pixels where there shouldn't be any. That was super nice of you to make that effort and it is appreciated by me even though you can't see the strap. You may want to try only adjusting contrast slightly. Again, just zoom in enough so the whole picture fills the screen. You may even be looking too hard for it. Just look at the overall box. There is a strap there.
I agree the box under the plane may not be Fred's sextant box, with a sextant still in it, for the reasons you say. That is a constructive and logical comment that Woody has already made, and I had said to begin with when I first posted the image.
In taking that comment into consideration, the box under the plane could still be the sextant box found on Gardner because there was no sextant found in the box on Gardner. In fact the box found was described as likely being latterly used only as a receptacle. That later use could have been a tool box before the last flight.
Even if it is only a tool box, not even an old sextant box, it still could have made it to the seven site, where it was dissasembled, the strap taken off and the wood part burned or lost. Note all of the supplies taken from the NC or gone now but there is a picture of them. Stuff on that island obviously gets scavanged or weathers away. Again I am not married to the idea that "the sextant box" has to be related to the clip. I do think a box or boxes with straps are easier to carry accross the island.
I do beleive the box under AE's plane, what ever it is for, could be related to the clip for the reasons shown in the latest PDF. It may even be a smoking gun(edit: in my opinion) if a better resolution image could be obtained