Here is a patch from ubuntu
Best regards
Charlie Smotherman
diff -Nru xtide-2.10/debian/copyright xtide-2.9.5/debian/copyright
--- xtide-2.10/debian/copyright 2009-11-24 22:49:43.000000000 -0600
+++ xtide-2.9.5/debian/copyright 2009-11-24 22:49:44.000000000 -0600
@@ -59,3 +57,6 @@
Commerce, January 1982.
------------------------------------------------------------------------
+
+The xtide icons are copyright 2007 Morten Kjeldgaard and are distributed
+according to the GNU Public License version 2 (or later).
