get random background image using php

I want to get a random background image using php. Thats done easy (Source):

<?php
  $bg = array('bg-01.jpg', 'bg-02.jpg', 'bg-03.jpg', 'bg-04.jpg', 'bg-05.jpg', 'bg-06.jpg', 'bg-07.jpg' );
  $i = rand(0, count($bg)-1); 
  $selectedBg = "$bg[$i]"; 
?>

Lets optimize it to choose all background-images possible inside a folder:

function randImage($path)
{
    if (is_dir($path)) 
    {
        $folder = glob($path); // will grab every files in the current directory
        $arrayImage = array(); // create an empty array

        // read throught all files
        foreach ($folder as $img) 
        {
            // check file mime type like (jpeg,jpg,gif,png), you can limit or allow certain file type   
            if (preg_match('/[.](jpeg|jpg|gif|png)$/i', basename($img))) { $arrayImage[] = $img; }
        }

        return($arrayImage); // return every images back as an array
    }
    else
    {
        return('Undefine folder.');
    }
}

$bkgd = randImage('image/');
$i = rand(0, count($bkgd)-1); // while generate a random array
$myRandBkgd = "$bkgd[$i]"; // set variable equal to which random filename was chosen

As I am using this inside a wordpress theme, I need to set the $bkgd = randImage('image/'); relative to my theme folder. I thought, I could do that using:

$bgfolder = get_template_directory_uri() . '/images/backgrounds/';
bkgd = randImage($bgfolder);

When I test $bgfolder, which seems to be the most important part, using var_dump() I receive a not working path:

http://yw.hiamovi-client.com/wp-content/themes/youthwork string(19) "/images/backgrounds"

Somehow there is a space before the /images/backgrounds/. I have no idea where this comes from! …?