From JSTOR:
On September 6, 2011, we announced that we are making journal content in JSTOR published prior to 1923 in the United States and prior to 1870 elsewhere freely available to anyone, anywhere in the world. This “Early Journal Content” includes discourse and scholarship in the arts and humanities, economics and politics, and in mathematics and other sciences. It includes nearly 500,000 articles from more than 200 journals. This represents 6% of the content on JSTOR.
This content, including images, may be used for any non-commercial purposes. Access to journals includes over forty Art and Art History titles, a list of which may be viewed in a PDF here. Access is provided through JSTOR’s website. Be sure to click Advanced Search and then check “Include Only Content I Can Access.” After searching, you can also limit to “Only Results with Images.”