When we upload our original pictures to Steem, how does the blockchain protect the intellectual property?
The Steem blockchain only stores text. You can’t upload pictures or any other binary files to Steem.
Ownership of copyright to a text can be protected by posting it to Steem in the sense that the post contains an immutable timestamp of the post. If you have made the post under your own name, you have a pretty good chance of proving the text was authored by you, if the text was first published at that time.
If your account name or anything posted with it indicates no particular identity, what you can do is prove that you control the private posting key of that account. Of course, you could’ve been voluntarily given the private keys of that account or you could’ve stolen the account keys before the real owner (and the author of the text in question) had noticed that and initiated account recovery (requires an old master key and an account recovery partner to confirm your identity by consenting to recovering your account). It then becomes a matter of weighing the evidence.
But I’d say that if you post under your own name and post things that tie the account to your real world identity, then your chances of proving being the originator of a particular text are pretty good if you publish that text on Steem first.