I've tried changing my profile picture and now the lock screen shows a profile picture there. Setting it to the previous one doesn't help. How do I get rid of the profile picture?
Solved by deleting ~/.face and /var/lib/AccountsService/icons/username.
This only works for a custom icon (when the
browse for more pictures option has been used). If one of the cinnamon-settings-users' GUI stock images is used, the file path will be /usr/share/cinnamon/faces/IMAGE.JPG . The easy way to resolve this is to switch to a custom icon and then delete the two files as described above.