It's cloth. Somebody's sleeve that got into the photo frame.
They're filming the fighter from the tailgate of something like a Lockheed C-130 Hercules, C-160 Transall, or Antonov AN-12 Cub cargo turboprop.
Note the nose-high angle of attack, and drooping leading edge slats as the Eurofighter slows down to approach the turboprop without stalling out. (Ask jet bomber and fighter pilots how much fun it was tanking up behind the old radial-engine KC-97 sometime...)
They could be filming a sales-pitch video, or something as benign as a high-definition video or IMAX movie. I'd wager that's the camera to the left of the gentleman near the tailgate.
