Guilt-Free Graphics

For example, I did a quick CC search of Cassowary and found THIS beautiful fellow.

Here is the place to search for Creative Commons images. After you've found one you like, go to its page and click on the "CC" symbol or "Some Rights Reserved" to find out what uses the author/photographer has granted.

My copy of Firefox has a Creative Commons search -- I can't remember if that's default, or if I downloaded it as an add-on from Mozilla.
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Note: as KilnGoddess of SquidU noted when I first posted this, if a photograph contains a picture of someone else's work -- e.g. a T-shirt design, a painting, a movie poster -- using that photo violates copyright, unless you get permission from the owner/creator of the image captured in the photo. A lot of people flag things with Creative Commons without realizing this.

Of course, if it's, say, an ancient Greek statue, the copyright ran out a couple thousand years ago. ;)

Edit: Someone complained that I was mixing up trademark and copyright, because I mentioned a carmaker's logo on the hood as an example of something in a photo which takes the photo out of public domain. I was unclear, yep. Trademarked logos are not the same thing as copyrighted images; they represent a company or brand, in addition to just being an "owned" image. Which means you're in even bigger trouble if you use them without permission.