Trying to add custom background image to Gregwar Captcha - laravel

Question

Here's my Utility/Captcha.php
i'm trying to add a custom background image to the captcha.
https://github.com/Gregwar/Captcha
Under API
setBackgroundImages(array($imagepath1, $imagePath2)), Sets custom background images to be used as captcha background. It is recommended to disable image effects when passing custom images for background (ignore_all_effects). A random image is selected from the list passed, the full paths to the image files must be passed.
I don't know how to set the file path to point to /img/captchabackground.jpg
What am i doing wrong?
<?php
namespace App\Site\Utility;
use Gregwar\Captcha\CaptchaBuilder;
/**
* Creating and Verifying Captcha
*/
class Captcha
{
public static function Build()
{
$width = 300;
$height = 50;
$char_number = 8;
$builder = new CaptchaBuilder($char_number);
$builder->build($width,$height);
session()->put('captcha',$builder->getPhrase());
return $builder->inline();
}
public static function Verify($input)
{
if (!session()->has('captcha')) {
return false;
}
if (session()->get('captcha') !== $input) {
return false;
}
return true;
}
}
<?php
namespace App\Site\Utility;
use Gregwar\Captcha\CaptchaBuilder;
/**
* Creating and Verifying Captcha
*/
class Captcha
{
public static function Build()
{
$width = 300;
$height = 50;
$char_number = 8;
$builder = new CaptchaBuilder($char_number);
$builder->build($width,$height);
setBackgroundImages(array($imagepath1, $imagePath2)),
session()->put('captcha',$builder->getPhrase());
return $builder->inline();
}
public static function Verify($input)
{
if (!session()->has('captcha')) {
return false;
}
if (session()->get('captcha') !== $input) {
return false;
}
return true;
}
}