It's like with code, scientific papers or with anything precious. Either it's so bad or common it's not worth stealing or it'll be stolen - eventually.
Physical security won't help because of always having a larger force (up to war weapons) to break the defence. Psychological security, e.g. by keeping it in your head or obscuring it (secret/password/...) won't help due to social engineering and us not being machines. Digital security? If it's shiny enough, it'll be pirated/cracked the next possible day once more than the creator has an access to it and if it's running.
- diamonds/gold/cash and visible robberies
- passwords and pulling the info from you over a beer or drugging you or resulting to violence
- software - heh, ask Adobe, Microsoft and others
- photo/video/DRM - decrypted, copied to others' profiles, impersonation or the old way of just dumping it to CD and selling on the streets
Don't try to prevent it because you never will once the thing is shared with more than one person. Instead, build your own "brand", your reputation, and eventually it'll be others recognizing your work even if somebody else steals it.
And also, some creators virtually mine on the stealing due to it increasing the popularity between people who wouldn't even consider buying, so for the next thing you come with they might be either more willing to buy or at least spread the word which might eventually get you the money, popularity or other things you might seek.