In this tutorial I’m going to show you a simple trick to change background using ‘PHP RAND’. So, every time you reload your page you will get different background… ok… let’s do it…

For this tutorial I’m going to use the WordPress Default Theme.

First, make some small images with different colors and save them into the image folder inside your theme. And make sure you add a number from 0 – 9. [In this case I made a folder call – bg – inside images folder & name the images as – image_0, image_1 …. ]

Then, use this snippet to generate random numbers. [You can add this snippet to your function.php file or in header.php file]

function genRandomString() {
    $length = 1;
    $characters = '0123456789';
    $string = "";
    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters))];
    }
    return $string;
}

After that, add this line of CSS code in your CSS file or in header.php file. [I’m going to add it to header.php file]

body {
	background: #d5d6d7 url('<?php bloginfo('template_url'); ?>/images/bg/image_<?php echo genRandomString(); ?>.jpg') !important;
}

final code looks like this...

That’s it… go back to the browser and hit reload…!!

Result

Hope you like this tutorial…!! Leave a comment if you have any questions… thank you.

PHP Reference : http://www.lost-in-code.com/programming/php-code/php-random-string-with-numbers-and-letters/