Well it's a bit more complicated than "that's a high-hat". The photo has a pretty good provenance. It's not like a Billy Meier photo that somebody went out and hoaxed, then show up with it. This photo originated in an aerial survey program run by the Costa Rican government back in the '70s and the object has always been known about for quite a while.
While it may remind some of a high-hat, the logistics of an actual high-hat appearing in this photo would be, well, complicated. It would suggest a high-hat somehow floating above the ground, but under the plane as the photo was taken, or double exposure of some sort in which a very tiny high-hat is somehow introduced to one frame of a large roll of film prior to it being developed. Sounds unlikely. Remember the actual object is very small in the actual frame of film. Here it is in the lower center "over" the lake:
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Note that this is frame 300. The RMK camera used had a film magazine with a spool of film loaded into it:
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So, one would have to gain access to frame 300 on a spool of undeveloped film in an attempt to create a double exposure inserting a tiny image of a high-hat.
It's possible that someone made copies of the original negatives or positives after they had been developed and cut into individual photos. They then doctored and/or created a double exposure with the copies, then replaced the original with the doctored copy in the archives. Seems a bit convoluted just to produce 1 supposed UFO photo.