Scenario: Not able to delete or set to default local Account Picture in Windows 10 (Settings > Accounts > Your account > Your Picture). Removed from https://profile.live.com but seems does not affect the local setting.
Go to “C:\Users\<USERNAME>\AppData\Roaming\Microsoft\Windows\AccountPictures” and delete the content(s) or;
Go to C:\Users\<USERNAME>\AppData\Local\Packages\windows.immersivecontrolpanel_***\TempState then;
Back to “Your account” setting, click on “Browse” and type in “C:\ProgramData\Microsoft\User Account Pictures\user.png” following with “Choose picture” button or enter.
*** not sure if this would be same or not, mine is windows.immersivecontrolpanel_cw5n1h2txyewy