You have the option of requiring students to agree to a simple anti-plagiarism statement when they submit an assignment.
To turn on the option:
Go to the course homepage.
Find the assignment and click the assignment link.
Find the Administration block:
Click Edit Settings.
Scroll down and click Submission settings to expand the options.
Change Require that students accept the submission statement to Yes.
Click Save and return to course (or Save and display).
Students will be required to select a check box confirming the statement when they submit the assignment. The statement is not sent to any third-party source to check for plagiarism. It is a simple confirmation by the student.