I just stumbled across this same issue - old scripts no longer silent.
Seems that there is a newer "-s" option
$ pngcrush --help |& grep -e 'silent\|quiet'
-q (quiet) suppresses console output except for warnings
-s (silent) suppresses console output including warnings
$ pngcrush --version
pngcrush 1.8.13, uses libpng 1.6.36 and zlib 1.2.11
...but pngcrush manpage only lists -q option
$ man pngcrush |& grep -e 'silent\|quiet'
-q quiet, the opposite of verbose.
.../Nemo
--
----------------------------------------- -----------------------------
earth native
