It's important that you look for images in the correct places (don't just do a Google image search!) to make sure that the images you find are high-quality and easy to reference. Below are some recommended sources to find images.
The Library subscribes to several image databases with high-quality images that you can search for. There are also free databases online which have a range of images you can search.
Searching or browsing websites with image collections is a good way of finding stock images, graphs, diagrams & infographics.
Government bodies & organisations often produce graphs & infographics from data and statistics they've gathered. Searching those government & organisation websites can help with locating images on the topic you're researching.