You are enabling users to perform image search from domains and websites specified in your custom search instance. 
Which Azure API will be an ideal fit for this?

Answer options:

A.Bing Entity Search API
B.Bing Visual Search API
C.Bing Custom Search API
D.Bing Image Search API

Correct Answer:C
Option A is INCORRECT. Bing Entity Search is not the correct choice because this API helps in searching the entities and places including restaurants, hotels, local businesses etc.
Option B is INCORRECT. Bing visual search lets us upload an image or use a URL to perform search and get information about it as required in the scenario.
Option C is CORRECT. Bing Custom Search API facilitates users image search from the domains and the websites mentioned in the custom search instance.
Option D is INCORRECT. Bing Image Search API helps us search and find images (static and animated).
References: 

https://docs.microsoft.com/en-us/azure/cognitive-services/bing-entities-search/overview
https://docs.microsoft.com/en-us/azure/cognitive-services/bing-visual-search/overview
https://docs.microsoft.com/en-us/azure/cognitive-services/bing-custom-search/overview
https://docs.microsoft.com/en-us/azure/cognitive-services/bing-image-search/overview