Why do sender and minter should be same on minting NFT?

Question

I am developing NFT marketplace with terra and I use CW721. And I noticed on mint function if the sender and minter is not equal it returns "Unauthorized" error. I can ignore this condition but is this required?

pub fn mint(
        &self,
        deps: DepsMut,
        _env: Env,
        info: MessageInfo,
        msg: MintMsg<T>,
    ) -> Result<Response<C>, ContractError> {
        let minter = self.minter.load(deps.storage)?;

        if info.sender != minter {
            return Err(ContractError::Unauthorized {});
        }
        ...
    }

In Javascript with Terra.js I sent request with my wallet address. But if the sender and minter must be same, I have to send request with minter's wallet address. And that means NFT creator should know the password of minter's wallet.

What's the difference between token_uri and image url? I think they are same.