The following errata for CentOS-2 have been built and uploaded to the centos mirror:

RHSA-2007:0992-01 Moderate: libpng security update

Files available:
libpng-1.0.14-11.i386.rpm
libpng-devel-1.0.14-11.i386.rpm

More details are available from the RedHat web site at
https://rhn.redhat.com/errata/rh21as-errata.html

The easy way to make sure you are up to date with all the latest patches is to run:
# yum update