This method is for the advanced user. It's easy to add huge numbers of photos by Ftp - and synchronization by Ftp is widely used - but again, by advanced users.
Read more about this feature in [ Photo → Add → FTP + Synchronization ]
The list of characters allowed can be extended using the config var: $conf['sync_chars_regex'] and its default value is '/^[a-zA-Z0-9-_.]+$/'.
To convert the pictures and albums created by FTP in a more flexible way: Virtualize
To generate the thumbnails associated with non-image files, put the representative picture in a folder /pwg_representative like this: