Here's the thing. No one here is going to write this essay for you, nor should they. As a senior in high school, you should see this as an interesting assignment and have some fun! Look around for a picture or photo that makes you feel something--makes you laugh or makes you sad, or makes you sigh, or whatever. It would help if the photo were from another era or taken in some unusual place. In these cases, the details and descriptions will be easier to identify. If not, if the subject matter is more commonplace, take care not to overlook the ordinary sensory images (the texture of the wool coat or the heat of the sunshine or the smell of the coffee in the coffee cup). Again, I encourage you to find an intriguing photo and enjoy the opportunity to reminisce.