Regarding the caching problem: It is your backend :P Just add some headers in your web server that tells the browser to not cache the image:

Cache-Control: no-cache, no-store, must-revalidate

I get your point. I think you also have to make some kind of business decision here: Do you want the people to visit your page because you can earn some money here with adds or other services or do you want to avoid that users have to switch the service? In the second case solutions are needed that can be integrated into steemit.com out of the box.