Reflective Writing
Unsplash like many others have said appears to have the best choice and variety of photo. I typically look for photos that can be widely representative. Age gender, race are not known… or are represented . Reflective Practice ( writing ) led to multiple images that can be used.
TweetExample for "Reflective Writing":
https://unsplash.com/s/photos/reflective-writing?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText