So many people today are using tags to organize photos and to upload them to sites like flickr for people to search. Most types of tagging are easiest to do on a computer, but certain types of tagging would make sense to add to photos right in the camera, as the photos are taken.
For example, if you take a camera to an event, you will probably tag all the photos at the event with a tag for the event. A menu item to turn on such a tag would be handy. If you are always taking pictures of your family or close friends, you could have tags for them preprogrammed to make it easy to add right on the camera, or afterwards during picture review. (Of course the use of facial recognition and GPS and other information is even better.)
Tags from a limited vocabulary can also be set with limited vocabulary speech recognition, which cameras have the CPU and memory to do. Thus taking a picture of a group of friends, one could say their names right as you took the picture and have it tagged.
Of course, entering text on a camera is painful. You don’t want to try to compose a tag with arrow buttons over a keyboard or the alphabet. Some tags would be defined when the camera is connected to the computer (or written to the flash card in a magic file from the computer.) You would get menus of those tags. For a new tag, one would just select something like “New tag 5” from the menu, and later have an interface to rename the tag to something meaningful.
As a cute interface, tag names could also be assigned with pictures. Print the tag name on paper clearly and take a picture of it in “new tag” mode. While one could imagine OCR here, since it doesn’t matter if the OCR does it perfectly at first blush, you don’t actually need it. Just display the cropped handwritten text box in the menus of tags. Convert them to text (via OCR or human typing) when you get to a computer. You can also say sound associations for such tags, or for generic tags.
Cameras have had the ability to record audio with pictures for a while, but listening to all that to transcribe it takes effort. Trained speech recognition would be great here but in fact all we really have to identify is when the same word or phrase is found in several photos as a tag, and then have the person type what they said just once to automatically tag all the photos the word was said on. If the speech interface is done right, menu use would be minimal and might not even be needed.