The images are being shared with other people as long as you keep your browser open. Once you close it, the sharing depends on other available peers, so the sharing stops once all the browsers are closed.
We depend on Webtorrent for browser support. That means we support Chrome, Firefox and Opera.
It's completely free and open source and the source code is hosted on Github.
We reduce hosting costs by being peer to peer, so the only expense we have is hosting this server on Digital Ocean, which costs $10/mo.