iPhones haven't seen too many design changes of late, apart from some difference in camera modules. Here is a quick look at all the rear panel of all the iPhone over the years:
Released in: 2007
Rear Camera: 2MP
Released in: 2008
Rear Camera: 2MP
Released in: 2009
Rear Camera: 3MP
Released in: 2010
Rear Camera: 5MP
Released in: 2011
Rear Camera: 8MP
Released in: 2012
Rear Camera: 8MP
Released in: 2013
Rear Camera: 8MP
Released in: 2014
Rear Camera: 8MP
Released in: 2015
Rear Camera: 12MP
Released in: 2016
Rear Camera: 12MP
Released in: 2016
Rear Camera: 12MP
Released in: 2017
Rear Camera: 12MP
Released in: 2017
Rear Camera: 12MP
Released in: 2018
Rear Cameras: 12MP + 12MP
Released in: 2019
Rear Cameras: 12MP + 12MP
Released in: 2019
Rear Cameras: 12MP + 12MP + 12MP
Released in: 2020
Rear Camera: 12MP
Released in: 2020
Rear Cameras: 12MP + 12MP