Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ab76609fab6493e2d5c6fac77a6a9b4d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563