Next step, I made a column in my Document Library and tagged my photos up to the third level, e.g. with "Blueberries".
So far so good, but now I'm stuck. What I can't figure out, and I hope you can tell me how to do, is how can I now filter my images also by the 1st and 2nd level, e.g. by "Fruits" or "Berries"? Any ideas?