<?php
// Configuration - Your Options
$allowed_filetypes = array('.jpg','.gif','.bmp','.png','.jpeg'); // These will be the types of file that will pass the validation.
$max_filesize = 1000000; // Maximum filesize in BYTES (currently 0.5MB).
$upload_path = './images/uploaded_images/'; // The place the files will be uploaded to (currently a 'files' directory).
$filename = $_FILES['userfile']['name']; // Get the name of the file (including file extension).
$ext = substr($filename, strpos($filename,'.'), strlen($filename)-1); // Get the extension from the filename.

// Check if the filetype is allowed, if not DIE and inform the user.
if ( ! in_array($ext, $allowed_filetypes))
    die('The file you attempted to upload is not allowed.');

// Now check the filesize, if it is too large then DIE and inform the user.
if (filesize($_FILES['userfile']['tmp_name']) > $max_filesize)
    die('The file you attempted to upload is too large.');

// Check if we can upload to the specified path, if not DIE and inform the user.
if ( ! is_writable($upload_path))
    die('You cannot upload to the specified directory, please CHMOD it to 777.');

// Upload the file to your specified path.
if (move_uploaded_file($_FILES['userfile']['tmp_name'],$upload_path . $filename))
    echo 'Your file upload was successful, view the file <a href="' . $upload_path . $filename . '" title="Your File">here</a>'; // It worked.
else
    echo 'There was an error during the file upload.  Please try again.'; // It failed :(.
?>

$upload_path = './images/uploaded_images/';

$files = scandir($upload_path);
foreach($files as $filename) {
    if(is_image($filename)) {
        echo "<div class='gallery-image'><img src='{$filename}'/></div>";
    }
}

function is_image($filename) {
    $image_extensions = array('jpg', 'jpeg', 'png', 'gif');
    $ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));
    return in_array($ext, $image_extensions);
}