Otis on ice. Personal photo.

This post is for marketing communications students and anyone looking to use free and legal images online.

With Google’s advanced image search  you can filter by licence to find images tagged as free to share, use and modify. Flickr will also let you search for images where Commercial use and mods are allowed.

The creative commons search tool will help you find images and other resources from a number of search services. Be sure to confirm the resource has a Creative Commons licence.

Pixabay is a service that provides images and videos that are free to use without attribution. Unsplash is a similar site offering free high-resolution photography.

Library of Congress photograph collection provides free images for non-commercial Wikimedia Commons is another good source.

Of course, you can always take your photo, or you can stylize text with a tool like Notegraphy

If you are looking for icons, one of the best sites I have found is the Noun Project.

Remember even though an image may be free for use and modification many licences require attribution.

Update: 
Here are a few more: 

• One from Sohee in the comments below: http://www.freepik.com/
• A Shopify article listing a number of sources 
• Here is an updated and much nicer version of the creative commons tool mentioned above 

I am sure there are many other sources out there, what have you found?