"It is the instructor's obligation to obtain clearance for materials used in class." (Getting Permission, 2007)
This applies to all materials, but expecially to coursepacks.
Many services are available to help clear copyright for any items - print or visual - that you think will need clearing. Probably the easiest is the UCSD Bookstore. A well used service is the Copyright Clearance Center.
A question to ask when pursuing copyright clearance is whether the permission is for print only or includes posting to a closed website for students.
When requesting copyright clearance, you can get permission for either a print or digital coursepack, but not both unless you want the students to pay for both types of clearance. Currently, the cost is just about the same whether you want print or digital; however, the system for seeking permission does not have a means of including both formats with just one permission.