Yes, your friend is right. I have never been in Vietnam. So I searched for information regarding this issue and I have found
General requirements:
1 - Face of the applicants must be at a neutral expression, without smiling or frowning.
2 - Your photos must be taken within 6 months of the application date. Dated stamp is not necessary but do not show a photo that is dramatically different from your current look.
3 - Photos must be taken against a white back ground and printed on quality photo paper.
4 - You can not wear any kind of glasses when taking these photos.
5 - Veins, hats and scarfs are strictly prohibited, and any other accessories that cover your ears or foreheads