praktik - i thought so as well but i have a bunch of other photos like this (same photo session i mean) without anything weird in the frame. if an artifact showed up in one chances are it would show up in another. i observed it with my eye for a split second. (and yeah, i was sober at the time). meh, the lens flares you posted all look at least vaguely like lens flares. i don't think this one does.
It is a lens flare because the "UFO" and the sun are exactly the same distance from the center of the image in both of the pictures. Zoom out a bit, draw an X from corners of the pictures, and you will see that the sun and the lens flare are exactly symmetrical.