Does not work with Memcache

Since RespImgPageCache extends DrupalDatabaseCache, you cannot use memcache for Cacheing... and if you are so unlucky to have both at the same time, you will have to remove the $conf['page_cache_without_database'] = TRUE; $conf['page_cache_invoke_hooks'] = FALSE; Settings so that memcache doesn't go ahead and save and pull pages... yet... they never get cleared.

To test:

Install Memcache module
Set up Memcache Module settings per memcache documentation
As an anonymous user Navigate to a page
In another browser window log in as a user
go to the page you navigated to in the Anonyumous user browser
Edit the Content and publish it
In the Anonymous user browser verify that you got a cache hit by refreshing the page
In the User Browser (or commandline) clear all cache
Refresh the page in the user window

The Expected results would be that the page refreshed... but since Since $conf['page_cache_without_database'] causes memcache to hijack access and doesn't give RespImagPageCache a chance, we are SOL.