Flying saucer over a football game in Liverpool

On February 14, 2015, during a football game, a spectator has photographed, without knowing it, a white and bright flying saucer moving at high altitude over the city of Liverpool, United Kingdom.

Witness report:

Watching my son play soccer and taking photos when I got home put the pictures on Twitter and on 1 picture only spotted an object in the picture which is not easily explained.