Another modX snippet,
this will grab all the images from a set folder and display them in a chunk

<?php
/*
::::::::::::::::::::::::::::::::::::::::
 Snippet name: ParseImages
 
Description:
    parses images in &folder in chunk &tpl
::::::::::::::::::::::::::::::::::::::::
Usage:
    [!ParseImages? &tpl=`myChunk_tpl` &folder='assets/images/folder'!]
*/
    //    $folder;
    //    $tpl;
    $output = "";
    $filesArray = Array();
    
    $imgDir = opendir ($folder);

    while ( $file = readdir( $imgDir ) )
    {    
        //checks that file is an image
        $file_type = strrchr( $file, "." );
        $is_image = eregi( "jpg|gif|png",$file_type );
        
        if ( $file != '.' && $file != '..' && $is_image )
        {
            array_push($filesArray,$file);
        }
    }
    
    rsort($filesArray);
    
    foreach ($filesArray as &$fn) {
    
        // set the placeholder 
        $params['image']=$modx->config['site_url'].$folder.$fn;
        $params['imagefilename']=$fn;
        
        // Parse the chunk
        $output .= $modx->parseDocumentSource($modx->parseChunk($tpl, $params, '[+', '+]'));
    }
    closedir ($imgDir);

    return $output;
?>