Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/42df0e6ebe9df55ea47f233b9dd6151f.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563