Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a762a8434d13a693d64c1a40b5f1a6e6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563