Here are a few website recommendations to get you started as you search for images.
The Smithsonian Museum has thousands of images from their museums which students and teachers can use free of charge
World Digital Library
This contains all kinds resources from around the world! You can search by place, time, and topic. All materials appear in their original languages, but descriptive text can be translated into 7 languages, including English.
Library of Congress
There are a number of resources here, from historic newspapers and maps to images and video.
The BBC has done a great job bringing together historical topics, timelines, and images.