This engraved picture of Veracini on the title page of his Sonate Accademiche is well known - and often presented as evidence for a chin-off technique in the mid-18th century. The picture is indeed remarkable for its depth of detail (a high resolution version is available at Library of Congress, here.). The thickness of the strings (pretty certainly still a plain gut g-string!), the old-fashioned form and position of bridge, the length and style of bow (long, relatively high tip, fixed frog) are all remarkably precise. What is slightly disconcerting are the apparent distortions - I can't get my left arm into the position depicted, I certainly can't get my right-hand thumb into that position, and the direction of bow-stroke is also a matter for concern.