My web hosting provider daily resets all folder permissions to 750, but since a few days, I’m having problems with uploading images inside wordpress. When change permissions of upload folders to 755, everything works fine, but it is reset the next day… The provider told me, that 750 should be fairly enough, and I think the same, but I don’t know how to do this with wordpress…
Use WordPress with folder permissions <= 750
The /wp-content/uploads/ directory needs to be writeable by the user that the web server runs under as when you upload files, it is the web server that is writing the new files to the uploads directory.
You need to change the ownership of the uploads directory to the web server user. The username and the method to change the ownership are somewhat dependant on the server set up, but your web host should be able to help you set the correct ownership on the directory.
The difference between 755 and 750 is that 755 gives everybody write permission for the directory, with 750 only the owner and group have write permissions.
http://codex.wordpress.org/Changing_File_Permissions