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]