When using images, it is your responsibility to use them according to copyright law and to observe the rights of the image's copyright holder.
Read the copyright statement or usage policy on each site before reusing any images.
Not all resources in this guide are copyright-free or in the public domain. However, many of these resources permit users to download the images for non-commercial purposes (such as lectures) as long as the source of the image is included. You may be required to ask permission, and possibly pay a fee, before using some images for publications or presentations.