I have used a purpose-made harness made by Irvin GQ for over 10 years.
It is a parachute harness with an adjustable length tether - BUT - the tether is releasable from the harness in emergency with a quick-release handle. The mechanism of this release is safe from accidental operation, but quick and easy if you need it.
The harness MUST be releasable quickly in case of ditching, fire, etc - AND the tether should be short enough to prevent matey from leaving the aircraft. The number of times I've seen people in a harness with about eight feet of rope at their feet FFS!! I remember an accident some years ago where the video cameraman was dragged along by his tether outside the helicopter after a hard engine-off run-on landing.
Also, in a small helicopter, the standard seat belt should still be used around the photographer's waist - a harness, even on a short tether is useless in a hard landing or accident (see above).
He's wearing the harness to keep him IN, not to catch him when he's fallen OUT.......