I found this image on the internet, why can't I just use it in my work?

Images that are available to download are not necessarily free to reuse, for example to include in an article or post on a website or on social media.

Check any copyright information that is available about the image. If you found the image via a Google search, you may see the statement 'Images may be subject to copyright'. This prompts you to look up the copyright status of an image and to ask for permission if necessary.
Many images are available under one of the Creative Commons licences, allowing you to use the image under the terms of the licence.
You may find other permission information in the website's "terms and conditions" or "legal notices" - often in a footer to the web page; for example, allowing non-commercial uses of the website's content.
If there is no information, you must assume that you need permission from the copyright owner and that the copyright position is "all rights reserved".
You should also ask yourself: Is it likely the person who uploaded this had the right to do so? People sometimes upload the work of others without permission. If there are serious doubts, it is not safe to reuse the material.
You may be able to use images for specific purposes under a copyright exception, for example for teaching or for criticism, review and quotation, as long as the use is fair dealing'. For more information, including some guidance on using photographs, see UK IPO guidance.