What does the document look like that is the last and final process to naturalization? How has it changed over the years?
If you google "naturalization certificate" and click the images button you will see a lot of 20th C certificates. They all have a photo of the new citizen. Then go back to google and search for "naturalization certificate 1870s" or some other decade in the 19th C and again click on images, you will see certificates that are much more plain. I tried to see if my great-grandfather's 1876 certificate would scan, but because it is framed the glass ruined the image.