I posted on the other forum about Mack's 1908 book
How to Play Baseball (the post encouraged the usual dialogue between Barry and me)
The book has a number of unique photos (unique to me, at least). This one of Mathewson I hadn't seen before, and it doesn't seem (again, to me) to look a whole lot like him. Perhaps it's just the cheap type 4 pulpy newsprint...
Max