This is from the official Steemit FAQ:

What are Steemit’s policies on plagiarism and spam?
If you are posting plagiarized or copied content, you can get in legal trouble for violating copyright laws. Plagiarized posts and spam are seen as abuse and will be downvoted by community members. If you are posting or using someone else’s content, you must ensure that you have the rights to use the content, and properly reference the sources where you got the material from.