unexplained sighting

Hello, I would like to report a strange object that I noticed after reviewing pictures I took of the scenery around lake "Lac de Matemale" in the French Pyrenees. In one of the pictures I noticed an unusual object, especially after zooming in. At the moment I took the picture, I did not see...

I thought I'd try here to see if anyone has any good idea for what I saw way back in April 1992 while visiting Costa Rica. Somewhere in a shoebox I have an old newspaper clipping with some details of what others saw that day, at least confirming I wasn't alone in seeing 'something'...