There are some basic rules relating to a caption that don't seem to change with time. The 5 "W's" have been around as a guide for many years.
It is not always necessary to include all of them due to the inherent nature and picture content/context. Repeating what is obvious from the photograph is considered bad practice.
Below is a selection of images with suitable captions. My experience in this field extends to some local newspaper work and although I provided factual information to my editor I was never asked to write the caption. The caption/cutline needs to be tailored to suit the story and in some cases suitable for the reader who may not wish to read the whole story, in which case it should include salient information. The cutline varies from the caption as it may run to a few sentences. Another important rule in caption writing is to never emphasise or suggest something that is not in the picture. The reader will loose confidence if they subsequently discover inaccuracies. I have given the photograph/caption combinations some context so that they can be judged within their published environment.
No 1 Local newspaper.
No 2 Monthly magazine article featuring Lincolnshire churches
No 3 Contents page for specialist motor sport magazine
No 4 Magazine article on classic car motor sport
No 5 Weekend supplement feature on wind farms and fishing
No 5 Specialist Paper Industry magazine article
No 6 Tourism supplement with local newspaper
Not the easiest of tasks without more direction on the type of publication the photographs will be shown with. The "W" rules when adhered to though give you the support to make the correct judgement, while being conscious of the pitfalls of being too creative and too descriptive of the obvious.