Upload profile image manually via FTP?

Hi there, is there a way to upload users profile photo manually via FTP. Which is the correct folder? I guess I have to add an entry in the database too … where?
Reason for that is, that the upload for some logged in users isn´t working (Error message) and because of custom coding its not possible to update the UM plugin itself.
Help is appreciated
Chris

The page I need help with: [log in to see the link]