When searching for artwork on the web or in a library database, keep in mind that it is best to go to the original source. The original source is usually the museum or gallery that has photographed the work. Subscription databases such as ARTstor will use and cite the original source. You want to provide the best possible image that is faithful to the original object in presentations and for inclusions in research papers. This is especially important when the artwork relies on color to convey meaning or that color is the primary mode of visual output, as in some abstract art.
Why is this important? There can be differences, sometimes extreme variations, on what an artwork looks like depending on who photographed it, what digital imaging standards were used (if any), or using and manipulating derivatives of the digital image. Some works are scanned from old slides, dated books, culled from other websites and changed to distort coloration, size, and clarity.
Ocean Park #19, Richard Diebenkorn, 1968, oil on canvas
From SFMOMA site
Blog found via Google Image
Don’t try to evaluate color and quality via your computer screen alone—your web browser, scanning device, screen or output configurations may not be set to optimally view images, so one computer may show a different image from another even if obtained from the same database. Rather, depend on the source.