You do not need to ask permission the copyright holder when you want to show multimedia in your classroom. The Dutch Copyright Act (Section 12(5)) provides an exception for educational purposes. A copyrighted work can be displayed or rendered without copyright holder's permission in the context of non-profit education. This applies to audiovisual works such as videos and television programmes, audio works and images. The display of the work must form part of the study programme, and must also take place physically within the educational institution itself.
Video: preferable use the databank Beeld en geluid op school.
Images: we strongly recommend to use only images with a Creative Commons license in your slides for you never know that you are going to use the slides in an Open Online course in future.