Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/37d563fca7b6b5f2f9c3fd2595c0a89b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563