Hi, Mr. Norton, I'll take a stab at this.........I've always thought Sam Chester resembled Booth, but not sure if he ever asked him for a favor that close to the assassination. Since this man does look like Booth, my first guess would be Sam Chester.
However, since I know Booth asked John Matthews for a favor, my second guess would be Matthews; using your clue, I've never seen a picture of Matthews in a book or at all.