"Wear a tuxedo for your ID photos." - Glenn O'Brien (TV Party, Downtown 81, the Style Guy)
I’ve always thought to go unkempt and unshaven.
This is so that I would be recognized from my passport if I was detained for several months in a sketchy country.
A decade ago, I was sent for a two-month business trip to China. I didn't have a valid passport (didn't need it within EU/Schengen Area) and had to make one in a hurry. I went to take my photo unkempt but freshly shaved. While in China, I didn't bother shaving, but I did get myself a haircut, that left me almost bald (communication mishap). One month in, I had to spend a weekend in Hong Kong to renew the work visa. On my way back, I happily handed my passport to the border control officer, and then spent terrifying 15 minutes trying to convince him, his colleague and then his superior, that the clean-shaved unkempt person in the photo and the near-bald, bearded person in front of them, are in fact the same person.