How To Enable Image Search In Google Custom Search Engine(CSE)

If the sites in your custom search engine include images, you can enable image search. Your search engine will display image results in a separate tab from web results.
Things to note:

• Custom image search results will vary from those returned by Google Images, even if you’ve configured your search engine to search the entire web. That's because Custom Search is designed to present a more personalized experience.
• Some features, such as Autocomplete and Promotions, aren't available for custom image search.