Collect all tags from images field and create a link list to then filter pages with images that have the selected tag

image_tags.php

<?php

/**
 * collect all tags
 * ======================================
 */

$alltags = array(); // container
$use_urlsegments = false;

// find all pages that have images with tags
$parray = $pages->find("template=basic-page|gallery, images.tags!=''");

// loop pages found and collect tags from images
foreach($parray as $p) {

    // find all images that have no empty tags, yeah you can
    // also use find on Pagefiles array!
    $images = $p->images->find("tags!=''");

    // loop them and add tags to array
    foreach($images as $im) {
        $tags = $im->tags;

        // convert "," and "|" to space and create array using explode
        if(strpos($tags, ',') !== false) $tags = str_replace(',', ' ', $tags);
        if(strpos($tags, '|') !== false) $tags = str_replace('|', ' ', $tags);
        $tags = explode(' ', $tags);

        // convert tag value to a page name using beautifyer, ü => ue, ö => oe
        // since special chars are not allowed in PW urls
        foreach($tags as $tag) {
            $alltags[$sanitizer->pageName($tag, Sanitizer::translate)] = $tag;
        }
    }
}


/**
 * generate links with tags as urlsegment
 * ======================================
 */

// make the array unique and create a tags nav from it
// add tags to the url of the page to later read it and
// render a list of pages

echo "<ul>";
foreach(array_unique($alltags) as $key => $tag) {
    if($use_urlsegments) {
        echo "<li><a href='{$page->url}$key'>$tag</a></li>";
    } else {
        echo "<li><a href='{$page->url}?tag=$tag'>$tag</a></li>";
    }
}
echo "</ul>";



/**
 * find all pages with the supplied tag
 * ======================================
 */

// enable url segments on the template if using url segments
if($input->urlSegment1 || $input->get->tag){

    if($input->urlSegment1) {
        $tagvalue = $input->urlSegment1;
        // get the original tag value text from the cached array
        $tagvalue = $alltags[$tagvalue];
    }
    if($input->get->tag) {
        $tagvalue = $sanitizer->selectorValue($input->get->tag);
    }

    // find pages with images having the requested tag
    $pa = $pages->find("images.tags~='$tagvalue'");
    if(count($pa)) {
        echo "<h2>Pages found</h2>";
        echo "<ul>";
        foreach($pa as $p) echo "<li><a href='$p->url'>$p->title</a></li>";
        echo "</ul>";
    }
}