array(
        'label'=> 'Select Box',
        'desc'  => 'A description for the field.',
        'id'    => $prefix.'select',
        'type'  => 'select',
        'options' => array (
            'one' => array (
                'label' => 'Option One',
                'value' => '?> <img src="<?php bloginfo('template_directory'); ?>/images/mainimage.jpg" title="" alt="" /><?php'
                                ),
            'two' => array (
                'label' => 'Option Two',
                'value' => 'another url to a different image will go here'
            ),
            'three' => array (
                'label' => 'Option Three',
                'value' => 'another url to a different image will go here'
            )
        )
    )