Change your Apple Account photo on iCloud.com - Apple Support
Change your Apple Account photo on iCloud.com - Apple Support
Can't change Apple ID account photo, keep… - Apple Community
"Can't change Apple ID account photo, keeps reverting to the old one again
I experienced this issue with my MacBook Pro. After wrestling with this for several days, I realized that the photo I was seeing was the one for my Mac User account, not the Apple ID account. When I updated the photo for the Mac User, the problem was resolved."
Summarized in this post by sberman at How do I update my iCloud account picture… - Apple Community
“Apple uses two distinct photos:
Your Apple Account photo. This is set at Settings > [your Apple Account] > Personal Information. You may change the photo at the top there.
Your Contacts photo. This is changed in the Contacts app at My Card. You may edit the card and change the photo there.”