This list provides links to the most common image search engines. Both Google Images and Tin Eye allow you to do a reverse image search by using the image rather than text to find similar or better images as well as more information.
Images from these sources wll be useful for a variety of disciplines.
Some museums have images that are large enough to capture for use in presentation tools such as PowerPoint. Others have images which are large enough only for reference. Check the ARTstor collections for large museum images to use in presentations and papers. Below is merely a selected list of museums with images on-line.
The following link takes you to a site with great examples of how to cite images using Chicago Manual of style in your papers. You can also consult the Chicago Manual in sections 12.31 - 12.51 for directions on how to write captions and credit lines.