pict2png is a simple PICT to PNG image converter, using a TIFF intermediate representation.
paint2png is a simple Mac Paint to PNG image converter. Source code is available as a pict2png branch.
Universal code-signed binaries are available in the releases section.
$ sudo cp pict2png /usr/local/bin/
$ sudo cp paint2png /usr/local/bin/
Usage: pict2png image.pict image.png
$ ls | while read f ; do pict2png "$f" "$f.png" ; done