How to install libpng and zlib
Open terminal by CtrlAltT
For libpng, run:
sudo apt-get install libpng-dev
For zlib, run:
sudo apt-get install zlib1g-dev
Ubuntu uses a thing called
apt, which is a package manager. It installs, manages, upgrades, and removes programs. If at all possible, you should try to install programs via Ubuntu Software Center. What you were likely attempting to do was install from source, which is only recommended if you know what you're doing.
Try to get out of the Windows mentality, which is to search google and download an installer. The Ubuntu Software Center searches Ubuntu's online repositories, which are generally guaranteed to work. Programs installed via Software Center or
apt will also be updated automatically by Ubuntu's Software Updater.
You can install libpng from the Software Center by searching libpng and choosing "PNG Library - runtime". Or from here libpng12-0 by clicking "available on the Software Center". Or using
sudo apt-get install libpng12-0 from a terminal.
zlib1g package should be installed automatically when you install
libpng12-0, because it is one of the
libpng12-0 package's dependencies. The package manager
apt installs all of a package's dependencies before it installs the package.