Display random images from folder with PHP without duplicates

I am trying to display a certain amount of random images from one directory on my website without displaying duplicates.

I found this question: Display 2 random pictures PHP with no duplicates which partially answers my problem:

<?php
$pics = array('image1.jpg', 'image2.jpg', 'image3.jpg', 'image4.jpg');
$images = array_rand($pics, 2);
?>

<img src="images/<?php echo $pics[$images[0]]; ?>" />
<img src="images/<?php echo $pics[$images[1]]; ?>" />

The problem I have is that the images are uploaded to the folder with completely different/random names such as 1a2265fg65444.jpg 55v4423097ww6.jpg etc, so I can't manually add them to the $pics array. I need to somehow scrape the directory for *.jpg and have the array generated automatically

I did try Michal Robinsons answer on Show Random images from a folder without repeating using JS or PHP but couldn't get it to print anything for some reason:

$all_images = glob("/your/directory/{*.jpg, *.JPG, *.JPEG, *.png, *.PNG}", GLOB_BRACE);

// shuffle($all_images); // uncomment this line to randomize the images

$images = array();

foreach ($all_images as $index => $image) {
     if ($index == 15) break;  // Only print 15 images
     $image_name = basename($image);
     echo "<img src='/public/directory/{$image_name}' />";
}

Perhaps I'm missing something?

Any pointers would be simply awesome.

Many thanks