Hi,

As https://www.libpng.org/pub/png/apps/pngcheck.html writes, pngcheck's
development has moved to GitHub. And there's a new 4.0.0 tag on GitHub.

https://github.com/pnggroup/pngcheck

Please update d/watch, and consider package 4.0.0.

diff --git a/debian/watch b/debian/watch
index a28a1af..f341cd3 100644
--- a/debian/watch
+++ b/debian/watch
@@ -1,3 +1,5 @@
-version=4
-opts="pagemangle=s{<A HREF}{<a href}g" \
-http://www.libpng.org/pub/png/apps/pngcheck.html ../src/pngcheck-(\d\S+)\.tar\.(?:bz2|gz|xz)
+Version: 5
+
+Template: Github
+Owner: pnggroup
+Project: pngcheck

Best regards,
Tianyu Chen