Sometimes you did not want to show default wordpress admin footer and want to replace with your text and logo. This example is for this purpose. So you can easily change wordpress admin footer without any big changes. You just need to copy paste below code in functions.php file.
//change the footer text
function custom_admin_footer_text () {
echo '<img src="' . plugins_url( 'images/custom-icon.png' , __FILE__ ) . '">Dummy text goes here.';
}
add_filter( 'admin_footer_text', 'custom_admin_footer_text' );