I'd love to know more about this poster, since it is over 100 years old!” The 16-by-20-inch poster, titled “Chums,” is signed by artist Percy Reeves.

One evening in late 1908, Henri Matisse introduced a short, dapper visitor to the community of often struggling artists who tended to congregate at the Bateau-Lavoir in Montmartre. Picasso was there, ...