One of the best resources for research-ready photos is the Chicago Face Database. This platform offers a wide range of images that are pre-tested and optimized for experimental use.
The photos vary in age, gender, and ethnicity, providing a diverse set for any study. Another excellent resource is the Karolinska Directed Emotional Faces, or KDEF.
This database includes images of individuals expressing different emotions, which is particularly useful for studies on emotional recognition or social psychology.
Wow! And doesn't this show the immense value of the Q&A Highlights section, and of Researchgate itself? If we'd had this when I was starting out 60 years ago why, Psychology would be sooo much more advanced by now!