[devel] Mention zlib-libpng license in each source file
diff --git a/png.h b/png.h
index 74388e8..2371192 100644
--- a/png.h
+++ b/png.h
@@ -6,6 +6,8 @@
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
*
+ * This code is released under the zlib-libpng license (See LICENSE, below)
+ *
* Authors and maintainers:
* libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
* libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger