Lens flare that looks suspiciously like a cigar-shaped UFO is not a UFO at all. The elongated object crossing the aviation contrail in the picture below is, because of its transparency, just a lens flare. The lens flare is on top of the rest of the photo, and despite that, you can still see the aviation contrail through the elongated object of light.
Furthermore, you can see a green transparent flare at the top of the picture, which is also a lens flare. This is typical for photography in sunlight or with the sun close to the subject in the photo. You can’t avoid them 100% if you’re photographing in sunlight. Artificial light or sunlight will, unfortunately, always reflect inside the lens.
The photo above is used in the article Cigar-shaped UFO in a stunning display above Denmark as part of the evidence that forms the basis for the claim that not a lens flare but a genuine unidentified flying object was immortalized in my photography.