The external test dependencies for CentOS specify libpng-dev as the package name for libpng-development. The correct name for that package on CentOS is libpng-devel.
In the file pts-core/external-test-dependencies/xml/centos-packages.xml, this bit
Code:
		<Package>
			<GenericName>libpng-development</GenericName>
			<PackageName>libpng-dev</PackageName>
			<FileCheck>/usr/include/libpng12/png.h</FileCheck>
		</Package>
should be
Code:
		<Package>
			<GenericName>libpng-development</GenericName>
			<PackageName>libpng-devel</PackageName>
			<FileCheck>/usr/include/libpng12/png.h</FileCheck>
		</Package>