Where to Find Free Images

Suppose you're writing a blog or creating some marketing materials, and you need some images to embed in your copy. Always make sure your images are free for commercial use.  The last thing your business needs is a lawsuit!  Here are some good resources for images:

Wikimedia Commons
Pixabay
Free Photo Bank
Freepik
Photopin
Openclipart
Freerange
Morguefile
Freedigitalphotos
Dreamstime
Microsoft Clip Art
U.S. National Library of Medicine
U.S. Department of Agricultural Research Service
Science Photo Library

My favorite inexpensive (but not free) site is:
Fotolia

Any other good resources I've missed?