No Pictures?

I was going through my posts last night and saw that some of the pictures weren't there anymore! There is just a big square with a minus sign in the middle! Does anyone know why that is? I took some time to add some of the pictures back in but didn't get to all of them. I'd hate to have to do that all of the time! I would appreciate it if anyone knows what I'm doing wrong that my pictures are going away! Thank you! ~~Pam