First, I wouldn't put a lot of stock in the provost marshal's descriptions of the pictures that generated the talk in the Rolla saloon. The PM was more interested in what Mr. Lowe actually stated, and not what the pictures purported to show. In other words, the PM may have got his description of the pictures mixed up, since it was not his primary interest in the case at hand. The pictures in question may have actually portrayed something different than what the PM recorded later.
Second, I have not seen books with illustrations about guerrillas that early in the war. That is not to say they did not exist, but I haven't heard of nor seen them. I do not know if the dime novels were around by February 1865, although it wasn't long after that.
What I am guessing caused the ruckus in the saloon were comments about a recent edition of the illustrated weeklies such as "Harper's" or "Leslie's." I see from an index of "Harper's" that in the 24 December 1864 issue were two illustrations on page 829 entitled "Guerrilla Depredations--Seizing Horses" and "Guerrilla Depredations--'Your Money or Your Life.'" I would guess that at Rolla, way out west, the 24 December issue may be rather new as of 13 February 1865, or at least may still be hanging around the town.
I am sorry I couldn't pin this down better than that, but illustrations of guerrillas intrigue me, as many of you know.