wget http://ftp.us.debian.org/debian/pool/main/libp/libpng/libpng12-0_1.2.50-2+deb8u3_amd64.deb dpkg -i libpng12-0_1.2.50-2+deb8u3_amd64.deb
If you experience problems with the installation, see this article: https://www.sysnettechsolutions.com/en/install-packet-tracer-ubuntu/