One of the most useful tools for image-related scholarly research is Artstor. However, be mindful of copyright restrictions - you can use them in your homework, presentations, password-protected education websites (Canvas), and personal use (inspiration) but you must research copyright permissions for each image for public use/publications.
The images found at these sites work well for art projects. Use them for research and scholarly papers only if you can verify that they are from a reliable source and have not been edited.
When using images for non-educational work, there are rules in place to protect the creator of the original image. The best thing to do is to find images through Creative Commons that allow modification.
Just like with the text resources (articles, books, websites) that you use, images have to be cited. This page from the Finding Images research guide provides information on how to cite images.
Finding Images: Image citation guide