Custom fields to image sitemap: only works if gallery is added to standard block

Regarding the structure of the sitemap for the custom fields galleries, I have adapted the code:

add_filter('seopress_sitemaps_single_img','sp_sitemaps_single_img', 10, 2);
function sp_sitemaps_single_img($imgs, $post_id){
	//Example with Advanced Custom Fields plugin
	//Replace get_field('test_img',$post_id) with your own custom field name
	if (function_exists('get_field') && get_field('image', $post_id) !='') {

            //get each id from the gallery
		$images = get_post_meta($post_id, 'image', true);
		preg_match('/\[gallery.*ids=.(.*).\]/', $images, $ids);
		$images_id = explode(",", $ids[1]);

            //loop through each id
		foreach ($images_id as $image) {
		$original = wp_get_attachment_image_src($image, $size = 'full', $icon = false);
		$alt   = get_post_meta($image, '_wp_attachment_image_alt', true);
		$html .= '<image:image>';
		$html .= "\n";
		$html .= '<image:loc>';
		$html .= '<![CDATA['.$original[0].']]>';
		$html .= '</image:loc>';
		$html .= "\n";
		$html .= '<image:caption>';
		$html .= '<![CDATA['.$alt.']]>';
		$html .= '</image:caption>';
		$html .= "\n";
		$html .= '</image:image>';
		$html .= "\n";
}
		return $imgs.$html;
}
		else {
			return $imgs;
		}
}

Each gallery image is now shown like this in the sitemap:

<image:image>
<image:loc><![CDATA[xxx/wp-content/uploads/2021/01/img_5409.jpg]]></image:loc>
<image:caption><![CDATA[test3]]></image:caption>
</image:image>

This looks better to me, although as mentioned in my original post, I’m not sure if it’s needed like this.

The problem that I need to add an image/gallery to the standard WP block still persists though. So unless there is an image in the standard WP block, it doesn’t recognize the images in the ACF field.

Thanks for your reply! I’m not running the plugin on a live site at the moment, just a local server. I have done this on a new install of WordPress with just ACF and SEOPress installed (and using a standard theme, Twenty Twenty-One).

I just added a WYSIWYG field to posts and inserted a gallery via Add Media -> Create Gallery in this field.

I was testing different SEO plugins and yours works the best for me – the only thing that doesn’t seem to work is indexing the custom field galleries.

Are you able to test this on your end or do I need to install it on a live site? Thanks

Many thanks – from a first look, it seems to work (I put in the checks before printing alt/URL)!