Show a Gravatar avatar when no photo is set in the contacts. This plugin was written by Folkert van Heusden (firstname.lastname@example.org).
Copy the files of this project to ../webapp/plugins/gravatar/ After that, users of webapp need to logout and login (once) to see the plugin appear under "preferences" -> "plugins". There, enable the plugin, click apply and logout + log back in.
After that, if a contact has no photo set the plugin will look for a photo/avatar on gravatar.com. If you do set a photo, it has precedence over any gravatar.com photos.