apt-cache policy libpng12-dev

libpng12-dev:
  Installed: 1.2.50-1ubuntu2.14.04.2
  Candidate: 1.2.50-1ubuntu2.14.04.2
  Version table:
 *** 1.2.50-1ubuntu2.14.04.2 0
        500 http://mirror.cse.iitk.ac.in/ubuntu/ trusty-updates/main amd64 Packages
        500 http://mirror.cse.iitk.ac.in/ubuntu/ trusty-security/main amd64 Packages
        100 /var/lib/dpkg/status
     1.2.50-1ubuntu2 0
        500 http://mirror.cse.iitk.ac.in/ubuntu/ trusty/main amd64 Packages

pkg-config --modversion libpng
1.2.50