The propaganda tends to be much weaker though. Purely he said she said stuff and everyone just believes it.
ISIS are "proven" to exist by a video of some dudes in the back of a pickup truck in a desert lol. That's pretty weak as far as proof goes.
They attempt to strengthen such weak proof with a staged bombing or two and next thing you know, people pull some serious mental gymnastics attributing said bombings to the pickup truck actors. :P