File:Keenan Walker NIH Profile Photo.jpg

Summary
According to Google, this image only appears on NIH.gov. A cropped version seems to appear on https://www.gottesmanlab.com/keenanwalker, but that can't be the original because it is cropped.

I found it on https://irp.nih.gov/pi/keenan-walker at https://i.irp.nih.gov/pi/2003157922.jpg, and it has no metadata saying anything else, so I think this is public domain because I think the NIH made it.