Wylio is a website that allows you to search for pictures that you can use without breaching copyright. They say they’re “the super sonic, thrifty, all-in-one picture finder, re-sizer and attribution builder for bloggers“.
You can sign up through your Google account for free (ad supported) or upgrade to a paid account (very cheap) to remove the ads. Here’s a video explaining (if it’s not showing click here to watch):
I did a search on the word “elephant” and it came back with 55,463 photos. I chose the picture below and Wylio gave me the option of downloading the picture or getting the embed code – which I did and copied below. This is the result – you’ll see the attribution below the picture and if you click on the picture, it links to the Creative Commons licence: