Google Art Project enables you to "explore museums from around the world, discover and view hundreds of artworks at incredible zoom levels, and even create and share your own collection of masterpieces." Find images to refer to and examine during your personal research, but do not include them in papers or presentations.
You can use the "Create an Artwork Collection" feature to save specific views artworks and create a personalised collection to use for your reference. You can add comment to each painting and share your collection with others.
HOWEVER, remember that these images are copyrighted! According to the site, "The high resolution imagery of artworks featured on the art project site are owned by the museums, and these images are protected by copyright laws around the world. The Street View imagery is owned by Google. All of the imagery on this site is provided for the sole purpose of enabling you to use and enjoy the benefit of the art project site, in the manner permitted by Google’s Terms of Service."