If you want to re-use material (typically but not exclusively an image, figure or table) that is published in print or online, you may need permission to do so from the copyright holder.
Your first step is to find out whether the material is indeed subject to copyright. It may not be - for example, it is published in an open-access journal or as an open-access article, it is published or made available under a creative commons license, or it is a government publications. There are also some open access data repositories (such as GenBank) that do not require permission to re-use.
Do not assume that the absence of a copyright notice means something is free to use - you need to find evidence that the material IS free to use!
Please be aware that in the majority of cases, you (or you students) need express written permission from the copyright holder to use survey instruments (questionnaires etc.) in your research. Many individual copyright holders ask only that you obtain permission and acknowledge them in any publications, including dissertations and theses, but some instruments require a fee.
IMPORTANT: obtaining permission to use an instrument does not give you the right to publish the instrument itself, or provide a link to it. Doing so is violation of copyright and can lead to legal action.