Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/26b1ed151dfe8f2c04f7e8341d6b54e3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563