LOC picture of the Lusitania returning from Europe after the 1913-1914 World Baseball tour, so Mathewson and Thorpe may have been aboard when the picture was taken.
The LOC collection on flickr is a timesuck. Friendfeed's John (aka dendroica) lured me in this time with a link to a picture of a Suffragette rally; then, poking around, found a Lincoln Steffens and some anarchist rallies, before this one dislodged me into looking into details of the tour.