Same as that really. For open tasks, photos of start and subsequent point, barographic traces and some start and fininh witnesses. For defined tasks, photos again including one of your taskboard showing where you have defined you are going. For speed tasks a data back camera set to match your barogarph time is needed. The FAI have a two sided form for World Records which is a good prompt for what you need.
Planning is the key so take time to understand the rules before the flight.
It really is a pity to not get a record ratified. They are witnesses, often other pilots who can sign and witness record and badge attempts. In Great Britain all PRS Pilot level pilots are OOs and using the prefix GB attach their BHPA membership number. If they are going to witness world records then they should get a copy of section 7 and probably speak to BHPA Records. Big one is not taking a start photo.