Here is the overview of Immigration and Visa counter at Ho Chi Minh airport where you pick up Vietnam visa on arrival:

Ho-Chi-Minh-City-Airport-Map-Arrival

The Vietnam visa procedure at Ho Chi Minh airport (Tan Son Nhat airport) is quite simple and straightforward. It normally takes 15 minutes to complete all the process upon arrival. However, in some case, it may take longer because of long traffic of passengers.

Photo service is available at Hanoi airport with around 2 USD/per photo.