Updating iptc content in photographs
The IPTC specification has been revised several times since it first appeared in the 1970's.
keywords and ratings are not IPTC; they are examples of custom metadata.
The IPTC Image and the IPTC Content panels in Photoshop's File Info offer a place to put lots of tags describing the image.
Some of these fields, such as Intellectual Genre and IPTC Scene, are for use with a controlled vocabulary that is most appropriate for newspaper publishing.
Each field has a notation of the intended use of the field.
Note that some fields, such as Photographer, appear in more than one panel.