A potential usage of an image should never be used as a keyword.
When people are keywording images, it's important to realize that the keywords should describe an image to somebody viewing the photo should use. Don't attach postcard to shots of a beautiful sunset. Don't use greeting card for a picture of a birthday cake.
If you are using these as a personal keyword, consider using a "collection" or "Set" in your image management application instead. That would be a much better usage. This way images don't get "Tagged" with poor keywords.