Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/64ade3b362b4009b556de77d6985e5e8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563