The way tags currently works, you can either select a tag or not, which makes it difficult to perform certain selection operations like find all pictures tagged "Landscape" but not "People". Simila\rly it is not possible to differentiate between all must be included or either may be included when selecting multiple tags. If I tag "Amanda", "Bob" and "Carly" does that mean that all these tags have to appear in every picture shown or just either of them?
I would like to suggest to use a tagging system that toggle between four values: Nothing meaning ignore this tag, "*" that means this tag must be included in every picture shown and "+" that means that any pictures containing this tag will be selected as long as all the "*"-marked tags are included too. Lastly "-" is used to indicate that a picture containing this tag must not included.
With these markers it is possible to make selections like "Landscape" with "Dennis" and either "Edith" or "Fabian" (or both) but neither "Gertrude" nor "Hadrian" in the following way:
This would solve a number of problems for me, at least.