Whilst sight seeing on a holiday in skiathos , we were to the far side of the island. visibility was excellent. there were military aircraft operating from the mainland at the time and were creating alot of noise but nothing to cause any concern. we did the normal taking of pictures ,admiring the scenery as it is stunning looking out over the sea. it's actually only recently when i set one picture in particular as my screen saver, that i noticed a blip. i zoomed the picture in to reveal a strange cloud like feature. its very prominent from the other cloud types . i can only estimate that it was at a height way too high for water sports and the distances to the mainland are greater than the picture may suggest. at the time i simply did not see the sight as it would have been indistinguishable.