My wife and I enjoy a very honest and open relationship. We're able to tell each other exactly what we like and don't like when it comes to sex and what turns us on, which is absolutely fantastic because we can share our deepest and darkest fantasies with each other without being worried about being laughed at or ridiculed for it.
A couple of years ago, I started taking nude photo's of her for my own use, and she liked it because she got to act all slutty which turned her on a bit. She could use big dildos and vibrators or vegetables while I took pictures and it made both of us quite horny. One thing led to another and I started to share these photo's with people online (with her face blurred or cropped out of the photo). I don't know why I did it the first time, but I know that every time I did, I got the biggest hardon I could imagine. Being open and honest, I told her about it, and instead of being mad about it, she was great and just asked what viewers thought about her.
From that original sharing, we got involved in sharing very explicit photo's with people we met online at the wife picture sharing sites (and usenet, if you know about that sort of thing). Over the years we've shared photo's and more recently videos with a few couples online, but only those we got to know really well.
One night, though, we got a bit drunk with some friends in real life, and admitted to sharing nude photo's and videos with strangers on the internet, and they admitted they'd done the same. Well, that took the relationship to a whole new level, and we started to share (if I'm honest, the husband and I shared) photo's of the wives via email.
Over a couple of months, things changed a bit, and we got comfortable enough to do a bit of nude hot tubbing with them one weekend, and things got a lot hotter from then on.
So much so that we started to have occasional 'game nights' whenever we visited each other. Nothing really intense, but more that we'd get a bit drunk and the ladies would occasionally flash us if they felt like it. My friend and I got to see a lot of the ladies' tits, and if we got really lucky, they would show off their asses and maybe even lift their skirts to show off their pussies (both of them shave!)