/**
 * Copyrightfeld
 */

function be_attachment_field_credit( $form_fields, $post ) {
	$form_fields['be-photographer-name'] = array(
		'label' => 'Copyright',
		'input' => 'text',
		'value' => get_post_meta( $post->ID, 'be_photographer_name', true ),
	);

	return $form_fields;
}

add_filter( 'attachment_fields_to_edit', 'be_attachment_field_credit', 10, 2 );

/**
 * Save values of Photographer Name and URL in media uploader
 *
 * @param $post array, the post data for database
 * @param $attachment array, attachment fields from $_POST form
 * @return $post array, modified post data
 */

function be_attachment_field_credit_save( $post, $attachment ) {
	if( isset( $attachment['be-photographer-name'] ) )
		update_post_meta( $post['ID'], 'be_photographer_name', $attachment['be-photographer-name'] );

	return $post;
}

add_filter( 'attachment_fields_to_save', 'be_attachment_field_credit_save', 10, 2 );