Here are some great sources for stock vector art and stock photography you can use for pretty much anything. The cover art (above) comes from Many Pixels.
Vector art is the kind that you can zoom in and it still looks smooth because it’s composed of lines and curves instead of little rectangles (pixels). You typically edit vectors with Adobe Illustrator, Corel Draw, Affinity Designer, Inkscape or Sketch. Here are some great sources for free vector art:
A great little collection of vector people.
Very nice collection of thematic vectors that can be colorized to match your theme or brand.
More beautiful vectors you can use with pretty much everything.
Need a perfect logo for just about any company? Brands of the World has them and they are free.
Some advice: Don’t just Google pictures and use the results on your next website or brochure. Instead, use royalty free artwork with an appropriate license for the use you have in mind. Here are some sources that have high-quality photos that are available in a way that won’t get you in trouble:
Some of the best stock photography on the internet and it’s made available so you can use the art on anything.
You have to incorporate these photos into your designs, but there a ton of great photos here.
You have to read the license block, but many of the photos are public domain or licensed using a permissive license. I often use Wikimedia when I need photos of a place or famous person.