Go to eBay and search "chicago postcards". About 4000 old ones will come up, with scenes going back to about 1900---you can browse the pictures for hours. (Or buy a postcard.)
Or download! Ebay has had some great photos of Chicago history over the years. A couple sellers have been selling off the Sun Times/AP photo files. I've downloaded thousands of photos. These photos had no watermarks.....many now do.