The josm-mapillary-plugin is released under the GNU General Public License v2 or later.

The GPL v3 is accessible here:
http://www.gnu.org/licenses/gpl.html

The GPL v2 is accessible here:
http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

Both licenses are also distributed with this software as the two files GPL-v2.0.txt and GPL-v3.0.txt.