To install imagemagick with PHP imagick extension on Linux CentOS you must follow these steps:

yum install ImageMagick.i386
yum install ImageMagick-devel.i386
pecl install imagick
At the end of the installation, create an inclusion file for imagick.so module and restart apache:
echo "extension=imagick.so" > /etc/php.d/imagick.ini
/etc/init.d/httpd restart
Test the correct loading of the imagick module with:
php -m | grep imagick