how-to place code in page title

You can count the gallery images inside the loop with this:

<?php
$item_count = '';
$gallery =  do_shortcode( $post->post_content );
if (preg_match_all( '/class=\'gallery-item\'\>/', $gallery, $matches ) ) {
	$item_count = count($matches[0]);
}
?>

Then you can add the count to your title like so:

<?php echo get_the_title() . ' ' . $item_count; ?>

This only counts the images in galleries, not the attached images (inserted in posts).

btw:
consider creating a child theme instead of editing your theme directly – if you upgrade the theme all your modifications will be lost.

Or put this in your themes functions.php and use the shortcode after your title in the editor “Foto’s ([gallery_count])”:

add_filter( 'the_title', 'do_shortcode' );
add_shortcode( 'gallery_count', 'add_gallery_count' );

function add_gallery_count( $atts ) {
  global $post;

  if(isset( $post->post_content)) {
  	$gallery =  do_shortcode( $post->post_content );
  	if (preg_match_all( '/class=\'gallery-item\'\>/', $gallery, $matches ) ) {
	  	$item_count = count( $matches[0] );
	  	return $item_count;
	 }
  }

}