Create category attribute in magento

require_once 'app/Mage.php';
Mage::app();

$setup = new Mage_Eav_Model_Entity_Setup('core_setup');

/*$setup->startSetup();
$setup->removeAttribute('catalog_category', 'categorytarget');
$setup->endSetup();*/

function createNewAttributeSet($name) {
Mage::app('default');
$modelSet = Mage::getModel('eav/entity_attribute_set')
->setEntityTypeId(4) // 4 == "catalog/product"
->setAttributeSetName($name);
$modelSet->save();
$modelSet->initFromSkeleton(4)->save(); // same thing
}

//Mage::app()->startSetup();
$setup->addAttribute('catalog_category', 'gemstone_image_hover', array(
    'type'          => 'varchar',
    'label'         => 'Gemstone Image Hover',
    'input'         => 'image',
    'backend'       => 'catalog/category_attribute_backend_image',
    'required'      => false,
    'sort_order'    => 99,
    'global'        => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
    'group'         => 'General Information'
));


echo "Success";