Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/df028d796e1f6eaeede91045c2c17ab2.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563