Hook sentence for an explantory essay on photography?
essay focuses on how to take a good photo, parts of camera, and invention of photography

I think starting out with a question that'll get the reader thinking is a good hook. 
Something like, "Are you really not photogenic, or do you just not know how to take a good photo?" 

I recommend not starting with a question unless it's a very strong, thought provoking one.

With that being said, something like the following would probably impress your teacher:

"Think about your favorite childhood moment. Now imagine being able to hold it in your hands forever. One photograph is all it takes."