Telegram's encryption is in-transit only. Telegram can see your chats on their servers.

You have to specify e2e, and it's not available for group chats. Durov, the founder of the system, got a lot of flak for using homegrown encryption. He has generally stood his ground on not releasing stuff, so I give him props for that.

It seems the only way to keep conversations and media private is end to end encryption with peer to peer topology.