I can't offer any advice that hasn't been given, but just want to mention that I can understand how the OP could have forgotten their password. It happens in legitimate circumstances and I can imagine it's very frustrating. It almost happened to me once and it was no fun.
I have my Exchange account for email/calendar on my iPhone for work (it's that or carry two phones, which I'm not a fan of) and due to my organization's security measures I have to change my password every 30 days, using 8 or more characters with at least a mix of capital and lowercase letters, special characters, and numbers. I can't use passwords that are similar at all to a number of previous passwords (I'm not sure what this number is, but I know its at least over 12).
One day back when I had my 4S last year I was trail running with a friend. It was early spring, we were at about 2,000 meters elevation, it was raining, foggy, getting dark, and we were a good 12 kilometers from the nearest civilization. I was feeling great, but in the low visibility my friend and I got separated. One of us made a wrong turn at an intersection of a few trails. I went to unlock my phone to check my GPX file for our pre-agreed upon route and to use the Find My Friends app to see where he was, and up came the "you must change your password" notice. I couldn't do anything except call an emergency number, but I needed the maps and apps on my phone to find my friend and also make sure we get back to civilization.
After trying futily for all the passwords of 8+ characters that I could easily remember, I was getting annoyed and worried that I would make a password and forget it, thus getting locked out of my iPhone like the OP. I keep daily backups so I wasn't worried about my data or photos, but the more time that went by the more worried I was getting that I wouldn't be able to find my friend. I didn't have a pen and paper with me, and the last thing you want to do in the cold and rain on a mountain is stop running, stand there and think through the most ideal password combination for your phone, all while getting colder and more separated from your running partner.
So I decided to make a new password and keep repeating it to myself until I could make a note of it in the notes app. Once I did that, I took a screen shot of the notes app with my new password on it and set it as my lock screen background and wallpaper. Not very secure, but that way at least I could use my phone until I got off the mountain and back home. If I didn't do this I'm pretty sure I would have forgotten my password by the next time I needed to use my phone.
Anyway, because I was able to use my phone I was able to find my friend and we got off of the mountain without any problems. That was the first time I ever thought about forgetting my password and it was disconcerting. So, TL;DR, OP I can totally understand where you're coming from and I hope you're able to get your data and photos back somehow, and also make sure to keep regular backups in the future.