One of the most useful resources for both artists and graphic designers are stock photos. Stock photos are images that are licensed for certain uses. Some sites like shutterstock require you to pay for the photos via monthly/annual subscription. However, there are sites that offer stock photos/images and videos for free, under a CC0 license, which means they can be used for personal or commercial use. Most sites stipulate that you cannot sell the unaltered image prints or as your own stock photos.
Below is a list of some of these free stock photo sites:

Unsplash.com
Pixabay.com
Pexels.com
Picography.co
Kaboompics.com
Magdeleine.co/license/cc0

There’s plenty of more sources for free stock photos. This is just a small list to hopefully help get you started! No matter what site you use, always make sure you read the FAQ or the license terms.

Typically stock photo sites will include photographs and vector images. There’s some that will also have stock video footage and even music! These resources can be used for a plethora of projects; business cards, art references, pamphlets, blog images, advertisements, and so much more. Personally I use them for references for my art and even as inspiration!