Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/a531d6ff51d6542c71c010d3a66337c3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563