Hi Caroline,
Quite right that the image of opium dens was a powerful one and was used by those anxious to close the door to Chinese migrants and to limit the rights of those already here. When you look at the Time/Life guide to telling your friends from the enemy, remember that until World War II America denied naturalization to both Japanese and Chinese immigrants.
An excellent book on the subject is The Coming Man, it's profusely illustrated with images from The WASP, yes there was such a periodical, and other publications.
At Amazon: http://www.amazon.com/Coming-Man-Century-American-Perceptions/dp/0295974532
The book's title comes from this image:
http://imgzoom.cdlib.org/Fullscreen.ics?ark=ark:/13030/tf7779p49j/z1&&brand=oac
.