Exclude images uploaded via meta boxes from Wordpress gallery

Question

I am using the following simple get attachment code to display all images attached to a certain post but I want to be able to exclude the images uploaded via a couple of custom meta boxes that are also attached to the post.

For example, how could I exclude an image uploaded with a meta key of sample_image_1 from this code?

<?php

    $args = array (
        'post_type' => 'attachment',
        'numberposts' => -1,
        'post_status' => null,
        'post_parent' => $post->ID,
        );
        $attachments = get_posts($args);
        if ($attachments) {
        foreach ( $attachments as $attachment ) {
        the_attachment_link( $attachment->ID , 'screenshot' );
    }}
?>

Answer 1

Get all of the attachment IDs from your meta fields, put them in an array, and pass that as exclude parameter of get_posts.

Answer 2

We can store the meta_key value in some variable suppose $metacheck and output the attachent only if the variable is not present.

        $metacheck = get_post_meta($attachment->ID, 'sample_image_1', false);
        //output only if metacheck has null value
        if (!$metacheck) {
        the_attachment_link( $attachment->ID , 'screenshot' );
        }