I've decided the first thing I need to do is organise my photos better!

I plan to put them in a box.

I'd like to make notes on the back of each about when, where and so on. So what kind of pen should I use so as not to affect the photo on the other side?

Alternatives are to write info on index cards between each set and use little post-it tags - but they could get separated from the photo and then I'd be back to square 1.

So can you recommend what kinds of pens work best for this?