If you want to get the base url of an admin, You can use one of the below code as your requirement.
Category: Magento
Magento is an open source based ecommerce web application that was launched on March 31, 2008. It was developed by Varien (now Magento Inc) with help from the programmers within the open source community but is owned solely by Magento Inc.. Magento was built using the Zend Framework. It uses the Entity-attribute-value (EAV) database model to store data.
Varien, the company owning Magento, formerly worked with osCommerce. They originally planned to fork osCommerce but later decided to rewrite it as Magento. Magento officially started development in early 2007. Seven months later, on August 31, 2007, the first public beta version was released.
Magento: Add image attribute of product
By using this you can create image attribute in product which is different as image gallery. It helps to tag the image over main image of product.