Ann, unfortunately, it seems to be associated with the Gravatar and possibly a google account. I have not found a way to add a photo here, and those photos that do appear were not uploaded here. Very annoying 🙁
I looked for a way but have not found one yet. If any WP specialist reads this and can offer a suggestion, you are more than welcome.
The best I know is through this site: https://gravatar.com/
However, I think that some places will let you upload one and be liked to Gravatar, which might be why their photo show up.