John Heartfield was a German Communist photomontage artist who were know as an outspoken critic of the Nazi regime, here some of his works:
Kaiser_Adolf.jpg
"Kaiser Adolf"
In this work he depict Hitler as the ex-kaiser Wilhelm II.
peace.jpg
"The man who took an oath to the German constitusion speak of peace, he will fullfil it as he done his oath"
Heartfield_salute.jpg
"The real meaning of the Hitler salute"
volk.jpg
"They will judge the people, as long as the people will not judge them!"
This was a reaction to a several death sentences to anti-Nazis that were giving althought the lack of solid evidence.