Searching for art, specifically images, is challenging because of the difficulty in describing art textually.
However, finding and studying art objects and images themselves is a great way to use primary sources to draw your own conclusions.
Check out the Reliable Websites page for some specific examples of websites that contain art images.
Additionally, depending on the type of art you are looking for, try finding some websites in the following categories:
Art gallery, museum, and library websites
Search engines and art repositories
For more subject specific image resources, take a look at Yale's Visual Resources guide.