There are search functions within Google that allow you to search for fair use photos and numerous free photo sites on the web. All of this is covered in training when you join Presto Media as a writer.
Fair use can be a bit confusing, but there are a few hard and fast rules -- NEVER use red carpet or paparazzi photos. Also, any photo watermarked by a photo agency (e.g., Getty, AFP) is a big no-no.
Figuring out fair use and where to get good, reliable photos takes time and experience. If you’re ever unsure of whether you can safely use a photo for an assignment, reach out to the editorial team and ask. It’s better than having an assignment sent back!