CIC do not require a certain number of photos for relationship proof, just include enough photos and other proof which leaves no doubt in their mind that your relationship is legit.
What I did was group photos by event, or location. I had about 10 photos each for major vacations/holidays, family events, parties, and your wedding if you are married.
All in all I had about 50 photos and to be honest that was probably too many. My other relationship proof was extensive.
A good tip is to write on the back of photos when it was taken, where, and who is in the photo. We were smart and actually had some close friends who were in some of the pictures we included write a supporting letter talking about us, our relationship, how they know us, etc.
I actually got copies made of photos so that it is not a loss if they are not returned to me.
Good luck!