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

// 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);
        $tags = explode(' ', strtolower($tags));

        // merge new tags array to the container
        $alltags = array_merge($alltags,$tags);
    }
}


/**
 * 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 $tag) echo "<li><a href='{$page->url}$tag'>$tag</a></li>";
echo "</ul>";



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

// enable url segments on the template for this page
// to get the url segment from tag links

if($input->urlSegment1){

    // sanitize the value
    $tagvalue = $sanitizer->selectorValue($input->urlSegment1);

    // 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>";
    }
}