Source: libpng Severity: serious with the almost started libpng transition, it is now pretty clear that libpng12 should be out of Stretch and libpng16 should be the default.
So, I'm opening this bug report to track the libpng12 removal. a better view will be after the transition is finished, but for sure only one libpng implementation can be ship with Stretch. cheers, Gianfranco