This bug is a slight generalization of Bug #321769.

Instead of having predetermined tags like comment 7 in aforementioned bug suggests, we allow users to write meta-tags, or "dynamic tags" as I would like to call it.

The user would create a meta tag that was based on a rule, on what photos should be tagged with this rule. The information processing, most likely will be based on EXIF data, but one could think of date / filename / etc influencing these meta tags.

This would be useful for a tag such as:
- Horizontal
- Vertical
- Unconventional crops
- Taken with my Nikon D40
- Summer

etc. Where each of the tags would tag photos based on what their EXIF data was like. The tags, instead of crawling the database every time, could clearly store what photos are in the tag, and change this information only incrementally.

The issue here is important: we are making tags more powerful than they are currently. The reason tags are super nice in the first place, is that they are a sort of generalization of folders, because one can't belong to multiple folders, but can to multiple tags. They have more information holding power.
By generalizing the idea even further, we can make them more powerful. The Mac's "smart folders" are like these dynamic tags, in that they are a search query that are saved as a folder. It would be a similar thing in f-spot, where the results of a query of "which of my photos are vertical orientation?" belong to the same tag automatically. The tags will be a way to make these queries, and save them for future access.