When posting things online or to a webpage, or even an image on a letter, we need to make sure that we are trying our best to use copyright free images. By doing so, we keep ourselves free from any misuse of copyright policies.
I spent a morning last semester listening to this very topic of copyright from the American Library Association. The speaker was very informative on copyright issues and also gave some thought as to what constitutes fair use.
I want to specifically focus on finding copyright free images today.
Go to http://images.google.com and type in something that you want to find an image for, such as 'horses.' When the image bar loads, you will see a button for "Search tools" on the right. From there you can choose "Labeled for noncommercial use" under "Usage Rights." See the screen shot below for your reference.
I hope this helps,
Have a great week,