The very serious Jim Elve references this news report that states Canadians must have neutral expressions in their passport photos (he might have cited a Canadian report):
"The International Civil Aviation Organization, ICAO, has released a recommendation regarding a new specification for photos in passports," explained Suzanne Meunier, spokeswoman for the Canadian Passport Office. "What they say is that the facial expression should be neutral ... no smiling, no laughing, no frowning -- no expressions, basically."
I had to renew my passport in Ireland, through the Canadian embassy in Dublin. I was apparently prescient, unknowingly satisfying these new requirements. I blurred a few data points to prevent forgery:
Customs people are always flumoxed when they try to run my passport through the reader. As you can see, it's not machine readable.