How to read pictures in a folder?

This can display a picture, but what should I do if I want to display all the pictures in the img folder? It doesn't work if I change it to $url = 'upload/'; So what should I do?

<code>header("Content-Type: image/jpeg;text/html; charset=utf-8");
$url='1.jpg';
$img = file_get_contents($url,true);
echo $img;</code>

Reply content:

This can display a picture, but what should I do if I want to display all the pictures in the img folder? It doesn't work if I change it to $url = 'upload/'; So what should I do?

<code>header("Content-Type: image/jpeg;text/html; charset=utf-8");
$url='1.jpg';
$img = file_get_contents($url,true);
echo $img;</code>

There are many methods, examples are as follows

<code>$dir = "upload/";  //要获取的目录
if (is_dir($dir)){
    if ($dh = opendir($dir)){
        while (($file = readdir($dh))!= false){
            $filePath = $dir.$file;
            echo "<img src='".$filePath."'/>";
        }
        closedir($dh);
    }
}</code>