Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6904e0921b3d136cc39ef5259bd9b3ad.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563