Plugin LMT, License Manager Tool, is not compatible with Piwigo 2.5 yet. That’s the bad news. The good news is that you can replace it with plugin Copyrights and plugin Perso Footer.
Plugin Copyrights lets you define licenses and apply them on photos. This plugin is much simpler than LMT because it relies on standard administration screens: Batch Manager gets new filter and new action, and you can also change the copyright on the photo edition screen.
Plugin Perso Footer lets you add a piece of text in your footer. Very simple.