Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2e8441f3d0e78c2d17dd86a0fd1dedab.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563