I really started editing my images for Olympics Games in Atlanta 1996 ( I was official photographer for sailing, shooting for ALLSPORT ). It's why I started to scan slide and neg, and I learnt a lot from that time.
Every morning I was first one in Media center in Savannah; and last one to go back to hotel. My english was not very good (not much better now) , and for every single image I had to do a caption telling a long story ( English way to do caption). It's where I started to really use the rule of 5W and H.
Few years before I spent some weeks at CFJ ( Journalism school in Paris , 35 Rue du Louvre, Paris.) for a Photo journalism course.
Our Professor was a great nice old photo-reporter. He pointed the fact that a photographer is reponsable for caption coming with his image.
I never forgot that.
And the best way to be correct is to use the 5W 's an H rule ( WHO, WHAT, WHY, WHEN, WHERE and HOW). Sometime it could be a pain, making your job longer. The way to write a caption is dictated by the audience . In general I always do a caption thinking that Photo desk in magazines and newspapers don't know the subject . If that image is used by a specialized magazine , it will not be a problem for them to have too many info.
Not everybody know where to find IPTC information in image and where is the caption. At Sea&Co we add a white stripe under the image where we put the caption. In that way we try to help Photos editors to have a confortable way to look at our production.
screen copy of a photo on Sea&Co server (here)
In each caption I try to have: Location name, Country, Name of the event ( with details of the event if possible) date, and who is on the photo. Names of skippers, Names of boats, start or finish for races , ...
In many case it's obvious , but 2 or 5 years after , when your are searching in archives will you remember what was names of boat, skipper? Record time?