As a bit of a follow-up to my post on some of our most-wanted requests, I thought I’d share a list of some of our most-helpful keywords. These are not so much subjects themselves as words that describe the image or the subject and help the researcher to narrow down the images more closely to what he or she is looking for.
For example, "studio" and "nobody" and "object" helped me narrow down over 10,000 laptop images to find this:

© Image Source Ltd / drr.net
instead of this:

© Hywel Jones / drr.net
Style-related words:
When searching for an image that will work well as a background "background" is an important keyword. Obviously many images can be used as backgrounds, but ones that are specifically created to serve as backgrounds (like marble or graphics) should be keyworded as such. A subset of those would be "textures", like wood, fabrics, etc.
As noted in a previous post, it is common for a buyer to request an image where the subject can be clipped out to go into a layout or composite with another image. "Cutout" and "object" are the most common terms, while "white background" or "plain background" are also useful.
Since most photographs are color today, it's also useful to note if an original is "black and white".
People:
The number of people is often important. Imagine the difference in a beach scene between one person enjoying a peaceful walk, and a big group having fun.
The most common and useful keywords are "nobody", "one person", "two people", "couple", "family", "three people", "group", and "crowd".
Very often the buyer also specifies a need for people of a particular age. Generally keywording down to the decade age gets us where we need to go: 20's, 30's, 40's, etc are the basics. For younger people "baby", "infant", "child", and "teenager" are good, plus the actual exact age is often important with kids and teens as they change so much in a short time. Sometimes broader terms like "adult", "mature", and "senior" can be useful, but it's just as easy and more specific and correct to keyword and search by the decade.
It's tempting, but counter-productive in the long run, to try to fudge a broader age range like 20's - 40's, because when the age is important, those images simply won't be considered even if they might actually be correct. If a broad range is acceptable for the search, it's easy to search on multiple ages or simply on "adult" or "mature", or "senior", etc.
The same is true with ethnicity. For ethical and legal reasons, as well as accuracy, only a person's actual ethnicity should be listed. Again, if an image is keyworded with every ethnicity a person "might be", it often will not get considered when the user needs a specific ethnicity. And if a broader range ethnicity is acceptable, that can either be left out of the search entirely or multiple terms can be searched.
There are many more useful keywords, and a bunch of non-useful ones too, and the various theories and practices of keywording and captioning can (and will) fill many more acticles, but this should be a good start to maximizing sales potential when these words are used correctly.
For more detail and a lot of good keywording ideas check our our Digital Railroad keywording guidelines.