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// CUSTOM ADMIN LOGIN HEADER LOGO
function so_custom_login_logo() {
  echo '<style  type="text/css"> h1 a {  background-image:url('.get_bloginfo('template_directory').'/images/logo_admin.png)  !important; } </style>';
}
add_action('login_head',  'so_custom_login_logo');

// CUSTOM ADMIN LOGIN LOGO LINK
function so_change_wp_login_url() {
	echo bloginfo('url');  // OR ECHO YOUR OWN URL
}
add_filter('login_headerurl', 'so_change_wp_login_url');

// CUSTOM ADMIN LOGIN LOGO & ALT TEXT
function so_change_wp_login_title() {
	echo get_option('blogname'); // OR ECHO YOUR OWN ALT TEXT
}
add_filter('login_headertitle', 'so_change_wp_login_title');