Hi, after prompting from Arch Linux, I've recovered the source code for pngtools from a backup and placed it on github at
https://github.com/mikalstill/pngtools.
I'd be happy enough to accept patches and bug reports there, and will do my best to service them -- noting that this code is nearly 20 years old.
I'm not sure what the correct Debian process is for such things, so I am just replying to this bug.
Cheers,
Michael