install pngcrush in centos5

1. wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.x86_64.rpm
2. rpm -i rpmforge-release-0.5.2-2.el5.rf.x86_64.rpm
3. yum install pngcrush

注意contos的版本：

lsb_release -a
LSB Version:	:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID:	CentOS
Description:	CentOS release 5.7 (Final)
Release:	5.7
Codename:	Final