Images are often an essential accompaniment to your research. They can support, deepen, and offer a visual anchor.
Clearing copyright of images is crucial for the ethical and effective use of images in your publications. This is not just a moral consideration, your publisher is not going to publish your research unless you are either using open access images or have cleared copyrights from the person who produced or took the image or their estate. As such, including images in your research publications could be a lengthy and costly process if not navigated and planned properly.
There are a large number of open-access site that can offer you the chance to choose visually appealing material with your research such as Google images or Flickr. Finding specific images is a bit harder.