SEARCH FOR:

$image_url = 'background-image: url(' . z_taxonomy_image_url() . '); background-position: left center; background-repeat: repeat;';

EDIT IN:

$image_url = 'background-image: url(' . options::get_value('styling' , 'cat_title_custom_image') . '); background-position: left center; background-repeat: repeat;';