Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/ab9c81b3b4aeec5d3b0fd502b42a90b5.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563