What are the next three letters in this combination? OTTFFSS

Need asap ! 1. someone at a party has just told a joke, and the photo shows a guest laughing uproariously with his head back, eyes closed, and mouth open. 2. photo of collection of vintage corvette convertibles at an automobile show. stock photography 3. photo of a mosquito filling the entire frame of the photo. 4. photo of the quilt-like appearance of grain fields taken during a ride in a hot-air balloon. 5. photo of the pollution of discarded cans, bottles, and other waste on a beach. 6. photo of the eiffel tower in paris, france. environmental photography aerial photography macro photography documentary photography stock photography candid photography