Add a custom field box to WordPress media files

2. Add custom field boxes to media files without a plugin

If you’re comfortable editing your theme’s functions.php file or building a custom plugin, you can add custom field boxes with code. This method is flexible and doesn’t depend on extra plugins.

Here’s how to do it:

• Open your theme’s functions.php file or a custom functionality plugin.
  
• Use the attachment_fields_to_edit filter to register a new field for media files. This filter lets you add extra form fields to the media edit screen.
  
• Use the attachment_fields_to_save filter to save the value of your custom field when the media file is updated.
  
• Optionally, display the field value on the front end by calling get_post_meta() with the media file’s ID.

Here’s a simple example that adds a “Photo Credit” field to media files:

// Add custom field to media edit screen
function add_photo_credit_field($form_fields, $post) {
    $form_fields[‘photo_credit’] = array(
        ‘label’ => ‘Photo Credit’,
        ‘input’ => ‘text’,
        ‘value’ => get_post_meta($post->ID, ‘photo_credit’, true),
        ‘helps’ => ‘Enter the name of the photographer.’
    );
    return $form_fields;
}
add_filter(‘attachment_fields_to_edit’, ‘add_photo_credit_field’, 10, 2);
// Save the custom field
function save_photo_credit_field($post, $attachment) {
    if (isset($attachment[‘photo_credit’])) {
        update_post_meta($post[‘ID’], ‘photo_credit’,
sanitize_text_field($attachment[‘photo_credit’]));
    }
    return $post;
}
add_filter(‘attachment_fields_to_save’, ‘save_photo_credit_field’, 10, 2);

After adding this code, a new “Photo Credit” field will appear when you edit any media file. The value will be stored in the database as post meta and can be retrieved anywhere in your theme.