I would actually look to the First World War for a theoretical basis in how official propaganda intersected with concerns about keeping up morale on the home front. There has been a ton of work, for example, on how propaganda intended for the home front specifically targeted women. Celia Kingsbury's For Home and Country: World War I Propaganda on the Home Front covers visual and literary images of women, as does Susan Grayzel's Women's Identities at War: Gender, Motherhood, and Politics in Britain and France During the First World War. A more basic overview of propaganda would be something like Gary Messinger's British Propaganda and the State in the First World War, which is more an overview of the state apparatus which produced it.

I'm less familiar with works that address this for the Second World War. Historians tend to be more interested in the First World War as the genesis of the state use of propaganda to affect attitudes about war. I'm also not too sure about whether posters is the biggest area of focus when it comes to WWII; film tends to be written about more, especially in the context of projects Hollywood completed for the U.S. government. Check out things like Robert McLaughlin's and Sally Parry's We'll Always Have the Movies: American Cinema during World War II or Clayton Koppes' and Gregory Black's Hollywood Goes to War: Patriotism, Movies and the Second World War from Ninotchka to Mrs Miniver.

One of the difficulties with a project like this is that it's notoriously difficult to gauge public opinion, especially when it comes to something like state propaganda and especially in wartime. How, for example, would the state determine whether or not a propaganda poster was "effective?" Could they determine that, or did they just think they could? Did it have a specific, conscious goal, and what was it? Just keep in mind that "propaganda" did not yet have a solid negative connotation in the early 20th century and was seen as a useful tool both by the state and by individuals.

EDIT: missing sentence, broken link.

If you haven't already, check out John Dower's book "War without Mercy." It's a fascinating read about the US campaign in the pacific and traces the evolution of American propaganda about the Japanese. For example, when Japan was rapidly conquering British colonial island holdings, the propaganda depicted them as "supermen," and "King Kong," to drum up public support. Later, after the battle at midway and the firebombing campaign of Japan, the propaganda switched to show the Japanese as louse and vermin, the implication being that those are pests that one should exterminate.