4. Use sites like Pinterest and Tumblr with caution.
I have read way too many terms of service over the last two months. And I'm not a lawyer, so the legalspeak can be confusing and I am NOT giving legal advice. BUT both Pinterest and Tumblr (and most other social sites) say that if you load something into their site (i.e. Pin It or Tumble it) YOU are claiming that YOU have a legal right to that picture. And if the owner of that photo comes after the company, you will be the responsible party. And Pinterest goes so far as to say if you REpin something, you're saying you have the right to that photo. Yes, if that's enforced, it would mean that 99% of people on Pinterest are doing something illegal. Will that ever come up? Maybe. Maybe not. But I'm leaning on the paranoid side now. I don't want to be the test case. And I don't want to pin something the owner of the photo wouldn't want pinned.
So pin your own photos, pin things from sites that have a Pin It button (see discussion in comments about the Pin It button, it's not always a safe bet either.) I pin book covers and movie posters because I figure that it's advertisement for said movies or books. But other stuff? All those pretty mancandy photos? I'm going to look but not touch.
*ADDED: Also see discussion in comments about posting and sharing pics on Facebook. Same rules apply.
5. Assume that something is copyrighted until proven otherwise.
That's your safest bet. If you're not 100% sure it's okay to use, don't. This includes things like celebrity photos. Someone owns those. There are enough free pics out there that you don't need to risk violating someone's copyright.
6. Spread the word to your fellow bloggers.
It was KILLING me not to be able to go tell everyone about all of this because I didn't want anyone else to get into this kind of mess. So if you know someone who is using photos in the wrong way, let them know. I wish someone had told me.