Hello!
Tell me, are there any logs of uploaded files to the server? Those. when users on the site upload pictures, etc. to the site from their PC, so that all this is written somewhere.
Thanks in advance!
See how they do it.
If by ftp, then you can see if your ftp server can detail the logs to files.
If via ssh - no.
If by CMS, then where does Linux come from - see what your CMS can log