Do you like to search Google for images to use as source content for your artwork? Do you worry about copyrights? Worry no more. Google lets you search for images based on usage rights, including images that may be “reused with modification”.
Simply (1) search from the Google Image search page (https://www.google.com/imghp) (2) Click the “Search tools” button and then (3) “Usage rights.”
Select the rights that are appropriate category.