To enhance your presentation, you may wish to use visuals. Here are some of the sources for items that are in public domain. That means you can use them without violating copyright laws or paying a fee to use them.
http://publicdomainarchive.com/public-domain-images/
http://www.stockfreeimages.com/p1/stock-free-images.html
https://search.usa.gov/search/images?affiliate=usagov&query