To determine if an illustration or photo is still protected by copyright, you can start by searching the Official Public Catalog of the US Copyright Office, which contains records from 1978 to the present. You can also search for a copyright notice on the image or on any accompanying materials, such as a book or website. The copyright notice should include the copyright symbol (c), the year of first publication, and the name of the copyright owner. If the image was created before 1978, you may need to conduct a manual search of the Copyright Office's records.
Another way to check the copyright status of an image is to look for a watermark. A watermark on an image is often a sign that the image is copyrighted and may include the name or company of the copyright owner. You can also try using an image copyright checker tool, such as Pixsy, to help you determine the copyright status of an image. It's important to note that just because an image doesn't have a copyright notice or watermark doesn't mean it's not protected by copyright. Many images on the web are copyrighted, but not all of them have the same usage requirements.