1- you can now apply in advance for Nepali visa online, fill-up the form, add your picture and print the page, show it on arrival, pay and receive your visa. as simple as that! http://online.nepalimmigration.gov.np/
2- If you don't have access to internet before your departure, don't worry... there are new machines installed at the airport before passport check, where you can fill-up the forms electronically, add your photo using the web-cam to your forms. Then you can submit your forms, machine will give you a receipt and with that you will go and take your visa from the desk.
3- Therefore there is no need of printed photo like before, although there is still a photo machine available at the airport.
4- You can pay your visa by dollar or euro or other currencies which I don't know.