Message # 1
Hey, i'm wondering why the photo module does not have the option that allows an entry to belong serval categories at same time?
This option would help me a lot.
Message # 2
Unsure why it is not available, but would guess it's to do with the 'belonging with several categories' is actually an artificial function. Entries (in other modules) actually always have a 'main' category they belong to and are artificially linked to other categories. I would imagine functions such as the slideshow button would only be able to show those entries that are not artificially linked.
The photo module does contain the filter functionality and the ability to 'mark a person or object'... Would one of these be an alternative to enable you to implement what you want.