Pitch the Pictures? Shorten Posts?

How can I make my blog more readable? Last class my group members discussed how long some of my posts were. They recommended making my entries somewhat shorter in the future, or if they were too long to add pictures. I would like to add pictures, but I am unsure of the copyrights on pictures which float around the internet. I don’t know what pictures are free game, and what pictures are not; could it be that as an unpaid, non-profit blogger, I can use any picture I choose? I don’t want to try my luck. And I don't know if shortening my posts is cheating my readers out of a good read or making a good read better.