And why does your physical presence have anything to do with their right to not share their own property? You did not take the pictures so why should you be entitled to them?
Snowdragon, I think I mentioned this upthread (so apologies if I'm repeating too much), but the way I see it is on a shared vacation, both parties have different skills that they contribute.
I'm not a great photographer -- I try, but usually my friend is better than me, and they seem to enjoy it more, so the general assumption is that I'll share their photos, and they're also welcome to any decent ones I managed. (And for me, I have no interest of photos with me in them, so the OP sharing only those wouldn't have been useful to me -- I like reminders of the pretty natural things we saw!)
I contribute other things, however: I'm good at reading maps, so I'm usually "in charge" of us not getting lost. I'm good at math, so I'm "in charge" of figuring out exchange rates and tips. It's just assumed that I'll take care of these things, since I'm the one with those talents. Both map-reading and math skills take time and education to develop as well; just because they're not artistic doesn't make them less valuable.
Another example: In my last trip, my friend was a terrible packer, so I let her put a bunch of extra stuff in my bag since we found out at the airport that hers was over the weight limit and would have incurred an additional $100+ charge. I could have just let her pay the $100 charge without offering up my space, but she was my friend, so why would I do that?
If the trip is like that, with both friends contributing in different areas, I see the sharing as more naturally assumed. It's very different than asking for photos from a trip the OP went on by herself, that the friend didn't partake in or contribute to.