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 # Publishing an extension on PEM
 
+## License
+
+A Piwigo plugin depends on Piwigo core. It relies on Piwigo core functions and is considered as a "derivative work" which implies being released under a GPLv2 compatible license. For example GPLv2 (obviously) or MIT.
+
+Even if you don't publish your plugin on PEM, please understand that your Piwigo must still be compatible with GPLv2 license. If you create a plugin for a client of yours, you have to publish is under a GPL-compatible license.
+
+## Actual publishing
+
 Once you extension is ready you can publish it via the <a href="https://piwigo.org/ext/" target="blank"> Piwigo extension manager</a> (PEM).
 
 Either create an account or login. On your user page, accesible via clicking on your username in the menu you need to add an extension with a name and a category