remove_action( 'propertyhive_before_search_results_loop_item_title', 'propertyhive_template_loop_property_thumbnail', 10 ); // remove default functionality
add_action( 'propertyhive_before_search_results_loop_item_title', 'propertyhive_template_loop_property_thumbnail_lazy', 10 ); // add bespoke functionality
function propertyhive_template_loop_property_thumbnail_lazy()
{
    global $post, $property;

    $photo_url = $property->get_main_photo_src( 'large' );

    echo '<img data-src="' . $photo_url . '" alt="' . get_the_title($post->ID) . '" class="lazy">';
}