https://steemit.com/faq.html#What_are_Steemit_s_policies_on_plagiarism

Plagiarism
The community is looking for you to add your own personal touch to your articles.

Plagiarizing, that is posting someone else's work as if it were your own, is very frowned upon by the Steemit community.

If you are using anyone else's material as part of your posts (including images) - please cite your sources.

Also, make sure that you are not violating any copyright laws if you are using someone else's material/images. Limited, sourced material sharing is OK under fair use and fair dealing doctrines