The Debian autobuilders build each package for various architectures. In the case of the perceptualdiff package, I enabled running the test script test/run_tests.bash during the build, in version 2.1-3, which includes changes beyond v2.1 up to 2a849e1 (6-Aug-2020). The tests succeed on some architectures (amd64, i386, arm64, ppc64el) but fail on others (armel, armhf, s390x).
I have no idea why. Likely something simple, like word size or endianity. Help / ideas welcome!
Details: https://buildd.debian.org/status/package.php?p=perceptualdiff