First, briefly define inference. How do you know an ambulance when you see one? What do see what do you hear. Why does an ambulance have a flashing light and siren? What do they tell you? What do you KNOW that you cannot see? What can you KNOW that you cannot see? Knowing without actually seeing is inference.
Use a picture that has something cut from it. Put the missing piece into the envelope glued to the back. What visual facts lead you to know what is missing?
Lead students to collect evidence on a chalkboard or transparency.
Display a large picture for the group. What can you tell from the visual clues? What time of the year is it? What is about to happen? How is life there different from life where you live? Your answers are inferences!