If you run a (recent) Linux, and you type `pngcheck` (with no arguments) what version number do you get? Feel free to respond with your Linux distro, if you want.
4.0.1
4.0.0
3.0.3
earlier than 3.0.3
Poll ends at .

@svgeesus If I had it installed it'd be 3.0.3:

~> apt list pngcheck
pngcheck/questing 3.0.3-3 amd64