The procedure to obtain Vietnam visa on arrival requires 2 passport-sized photos.  Here are the detailed regulations for the photographs:

– Photographs should be 4 x 6 cm (Vietnamese standard photo size) or 2 x 2 inches in size, identical, taken within the past 6 months.
– The photographs must be in color, printed on bond paper or professional photo paper
– They must be full face, front view with a plain white or off-white background.
– A hat or headgear must be kept out to avoid obscuring the hair or hairline.
– The outfit with the exception of religious attire should not be worn.
– In some special cases, consistent objects like prescription glasses, a hearing device, wig or similar articles are still accepted
– Dark glasses or nonprescription glasses with tinted lenses are not acceptable unless required for medical reasons.

Please prepare 2 photos as styled as above requirements to avoid any hassle at Vietnam airport. In case, you do not have time to prepare 2 photos in advance, you can get them directly at the photo store of Vietnam airport. It costs around 2 USD.