Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b993d5dba6bb9a09d5cccee2ad5d5bdf.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563