On BowerBird, we give you the ability to caption all images. You have a 'Title' and a 'Description' field.
The title should be simple and descriptive, i.e. 'Bedroom 1, first floor', or 'Kitchen looking North into Garden'. The caption is then where you add further details.
While captions are really yours to use as you wish, the things that journalists are definitely looking for are:
Location: what part of the building is the photo from? How does it relate to other spaces? For instance, does the kitchen open onto a patio that is out of shot?
Details: what are they looking at? For instance, are there architectural details that are worth mentioning?
Deeper story: what's interesting about this photo? Was it a tricky part of the design to negotiate? Is it your client's favourite place to sit of a morning?
Products: highlight the main products shown (materials, appliances, finishes etc.) as editors will often ask for this.
The more information you provide at the beginning, the less work you'll need to do when journalists ask for more. They'll love you for it!