The source of this image is the Wikimedia Commons. Muchas works entered the public domain in 2010, for he died in 1939 and the copyright expired seventy years after the death of the creator.
The image above is from the Czech art noveau painter and decorative artist Alfons Maria Mucha (known in English as Alphonse Mucha). A list of his works can be found here. I especially like his stained glass window for the St. Vitus Cathedral in Prague