One? Twelve? Twenty? How many pictures should you use on your layout? The rule is: there are no rules! Really! You just need to decide what is right for the story you want to tell.
In this age of digital cameras, we are no longer limited to the amount of photos that we can take, save, and print...
I have actually found a buck or two sometimes just walking in a parking lot. I pick it up of course. Even though it's only a buck, I look around quickly to see if anyone is nearby that might have dropped it. Walking through parks I've found everything from backpacks to ballcaps, to pens. But what this person found is a true treasure!