After looking at expensive and complicated software to aid in performing this task I finally found what I believe to be a very good solution. The price cannot be beaten - it's free, with the restriction that you not perform a service for pay with the software. As far as using the software is concerned, I don't think it could be any more simple.
Go to http://arcurs.com/keywording/index.php The key-wording tool consists of one blank data field, one drop-down list with three options and a "Search". Type in one or two words that describe the image you are key-wording, select weather you want to consider all images, photos only or illustrations only and click the search button. Based on your description you will get a page of image thumbnails. Simply select the images "most like" your image and click "Accept chosen images and proceed to keyword selection".