php Setting background image randomly from folder

I am trying to randomly set the background image of a webpage from a folder via PHP.

I have the following code:

<!DOCTYPE HTML>
<html>
    <head>
        <link rel="stylesheet" type="text/css" href="style.css">
        <title>404</title>
    </head>

    <body id="Background404">
        <p>404-Page not found. <a href="http://url.com>Home.</a></p>
    <?php
        $dir = '/var/www/html/Images';
        $fileNames = array();
        if(is_dir($dir)){
            $handle = opendir($dir);
            while(false !== ($file = readdir($handle))){
                if(is_file($dir.'/'.$file) && is_readable($dir.'/'.$file)){
                $fileNames[] = $file;
                }
            }
            closedir($handle);
            $fileNames = array_reverse($fileNames);
            print_r($fileNames);
        }
        $totalLength = sizeof($fileNames);
        $randInt = rand(0, $totalLength);
        $randFile = $fileNames[$randInt];
        echo '<style> #Background404{background: url($randFile);}</style>';

    ?>

    </body>
</html>

Note: the printing of the files is just to ensure I reach that point in code and to see what the files are called. I found a similar question here: Random Background Image PHP but when I used that answer I got just a pure white background.

Here is a copy of printed array:

Array ( 
        [0] => GraniteBridge.png
        [1] => mobileBackground.png
        [2] => OtherKingdom.png
        [3] => NetherBase.png
        [4] => BackgroundTablet.png
        [5] => Snowy.png
        [6] => Village.png
        [7] => background2.png
        [8] => CactusFarm.png
        [9] => FrontView.png
        [10] => CreditsPortal.png
        [11] => FrontNight.png
        [12] => background4.png
        [13] => XPFarmRailway.png
        [14] => GoldIronFarms.png
        [15] => Pyramid.png
        [16] => NetherFortress.png
        [17] => TheEnd.png
        [18] => Library.png
        [19] => Background.png
        [20] => twitter.png
        [21] => mobileBackground1.png
        [22] => mobileBackground2.png
        [23] => BirdsEyeView.png
        [24] => EndPortal.png
        [25] => AboveVillage.png
        [26] => TowerToTheHeavens.png
        [27] => TowerArmorStands.png
        [28] => FullSizeBackground.png
        [29] => Mansion.png
        [30] => Night.png
        [31] => Dojo.png
)

Solution

You can use array_rand to get a random index in the array. Then you can use that random index to get an image from your array

$randomImage = $images[array_rand($images)];

This is a complete example which uses glob to fetch the images in the folder

<?php 
$imagesDir = '/var/www/html/images';
$images = glob($imagesDir . '*.{jpg,jpeg,png,gif}', GLOB_BRACE);

$randomImage = $images[array_rand($images)];
?>

<img style="background-image:url('/path/to/images/<?php echo $randomImage ?>');"/>