Q: I developed an online version of my course. What is the best way to provide copyright protection at the time when students sell notes to commercial notetaking services?

A: Some faculty include a statement to the syllabus forbidding selling/buying class notes, exercises, quizzes, exams without their written permission. There are no tools to monitor the infringement of copyright when students sell notes to commercial notetaking services (FlashNote/Noteutopia/Notehall, Course Hero etc.).
Copyright protection for online course materials is a grey area. Is it legal or ethical?
There are "legal issues and the general controversy around selling class notes. Notehall and competing platform Course Hero even received a cease and desist letter from the UCSC general counsel, and it also alerted faculty members and undergraduates that the commercialization of class notes is illegal in California." 

Q: How do I check students papers for plagiarism?

A: There is Plagiarism Checker Tool: http://www.plagiarismchecker.com/help-authors.php

You can download it for free: http://www.plagiarismchecker.com/

or Turnitin

https://turnitin.com/static/products/index.php

Turnitin is very powerful but it is not free.

Look for the plagiarism checking tools incorporated into the LMS platform you use. For example, you can create Safe Assignments using Blackboard.
SafeAssign checks all submitted papers against the following databases:

• Internet - comprehensive index of documents available for public access on the Internet
  
  
• ProQuest ABI/Inform database with over 1,100 publication titles and about 2.6 million articles from '90s to present time, updated weekly (exclusive access)
  
  
• Institutional document archives containing all papers submitted to SafeAssign by users in their respective institutions
  
  
• Global Reference Database containing papers that were volunteered by students from Blackboard client institutions to help prevent cross-institutional plagiarism.

Blackboard Help Articles

• About Safe Assignments
• Create & Edit Safe Assignments
• Grade & Manage Safe Assignments
• Understanding Originality Reports
• Direct Submit a Paper for Plagiarism Check

Top 10 FREE Plagiarism Detection Tools for Teachers

Google offers a Scholar Plagiarism Search tool to search " not only plagiarized phrases but also correct missing quotation marks and citations. This software scans your research paper, essay, coursework or dissertation completely from its database of internet resources, past exam papers, past essays, old dissertation papers and published journals."