Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/75e7b2c58f2b567897154d52e37ca940.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563