There are a lot of options out there for finding free images, and below are just a few websites that offer royalty free images for public use. Always be sure to check the individual images for attribution requirements.

You can also use Google Image Search, but if you choose to go this route, make sure that under Search Tools you change the option for ‘Usage Rights’ to ‘Labeled for reuse with modification’ so you’re getting images that are either public domain or Creative Commons.