This Tip Show How to Install Gimp Registry/Save-for-web Plugin on Linux Mint 13.
The Content give Focus Only to the Essentials Instructions and Commands to make it Easier to Follow.
Solution:
sudo apt-get install gimp-registry-plugin
$schemamarkup = get_post_meta(get_the_ID(), 'schemamarkup', true); if(!empty($schemamarkup)) { echo $schemamarkup; }