Wen you enable cache, the pages will not refreshed each time when you uploads a new image. You can test whether cache is working for you or not by enabling the cache print messages.
Change the below line in include/constants.php
define('PRINT_CACHE_MESSAGES', 0);
to
define('PRINT_CACHE_MESSAGES', 1);
but make sure you turn it off also after your testing
Also, you need to clear all the caches periodically by using cache plugin in your ACP.