Definition of ideology can be found in Glossary, which is part of question 1.
The ideology of an individual can shape the way you view and agree or disagree with this image. This visual text has a very obvious opinionated view. The image states a anti-war stance and therefore is opinionated. The ideology of someone will therefore decide whether they agree with image or not, for example, if I was pro- Vietnam War i would disagree that the U.S should stop the war against Vietnam because my ideology is that we were doing the right thing in Vietnam.