I talk about copyright I always encourage teachers and students to use their own images when they need to include visuals in a paper or presentation. If you don't own an appropriate picture then look for images that are in the public domain. While Google Docs does have a built-in image search tool, Google Images is far from the best place to find images that are in the public domain. Pixabay and Unsplash are better places to find public domain images. If you need to use images in a Google Document, both of those sources are accessible through Google Docs Add-ons.
Pixabay for Google Docs is a free Add-on created by Learn In 60 Seconds. With this free Add-on installed you can quickly search for an image. Search results appear in the right hand margin of your document. Double-click on an image to insert it into your document. You can resize the image just as you would any other image that you upload to a Google Document.
Full Deck for Google Docs is a free Add-on that uses Unsplash to locate public domain images to use in your documents. Once you have found an image that you like, click the insert button that appears just below it. Like the Pixabay Add-on, you can resize your selected images by clicking and dragging the borders.
Join my G Suite for Teachers course to learn more about using Google Docs in your classroom.