|There were some paste-in photos in the old Fourteen Leaflet, and a page of half-tones in an issue of Fantasy magazine, but photographs were little seen till 1939 when LeZombie, Speer, and others began publishing them. Photos were most often of fans and fan activities, but also included tabletop fantastic scenes, shots off the screen of fantasy movies, and whatever else might be of interest. By the 50s expanding size of mailing lists had made actual use of tipped-in photos impractical, but long before this Ackerman's Assorted Services lithographing, and Tucker's discovery of a half-tone mimeo process, had opened up new possibilities.
from Fancyclopedia 2 Supplement ca. 1960:
Tucker's process was not really Stenafax, but a chemically-treated stencil. Hal Shapiro claims to be the first to bring Stenafax to fandom's attention; he was in the process as editor of a mimeoed Air Force paper, which received Stenafaxed items (the device uses an electronic stencil-cutting needle to reproduce a black-on-white master copy) from AF journalism HQ.