Posters played an important role during World War I, even before the outbreak of revolution in Russia in 1917. Along with newspapers and pamphlets, posters were an efficient means for governments to communicate--and persuade--their populations. This was true in Imperial Russia no less than elsewhere. The tsarist government used propaganda art to foster patriotism, dehumanize the enemy, and encourage support for the war effort.
There are a number of fantastic online sources of propaganda art during the First World War. The Harry Ransom Center at UT Austin has digitized hundreds of pieces of art, including many from World War I. Sort them by language and you will find a number of Russian posters at the end of the list. Depending on your topic, you might even find something that would be useful as an additional source for your research this semester.