Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/8d3c2b43f29f8e5f1495c6716c1d7915.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563