gistfile1.php

<?php
/* Add a checkbox to the featured image metabox */

add_filter( 'admin_post_thumbnail_html', 'theme_featured_image_meta');

function theme_featured_image_meta( $content ) {
    global $post;

    // Text for checkbox
	$text = __( "Don't display image on post.", 'textdomain' );

    // Meta value ID
	$id = 'hide_featured_image';
	$value = esc_attr( get_post_meta( $post->ID, $id, true ) );

    // Output the checkbox HTML
    $label = '<label for="' . $id . '" class="selectit"><input name="' . $id . '" type="checkbox" id="' . $id . '" value="' . $value . ' "'. checked( $value, 1, false) .'> ' . $text .'</label>';

    return $content .= $label;
}
?>