A Canadian citizen can enter the US with proof of citizenship plus government issued photo ID. I usually use my birth certificate and driver's licence rather than carry my passport. A naturalized citizen would have a citizenship card which has a photo on it. Non-Canadians are subject to whatever rules apply to their country of citizenship.
I'm thinking that these guys probably crossed at multiple points of entry simultaneously or close to it, by land, maybe even by different methods. I'm thinking that most were probably on transit rather than in private cars because the INS officer must take into account that a prolonged search will hold up a bus or train full of people. Plus, I would hope that if they had cars that the details and licence plate numbers would be published. I think planes are unlikely because airlines must turn their passenger manifest over to security and they can run a check on everyone on the plane before it lands, when they bought their ticket, how they paid, etc. I don't think that is the case with bus or rail passengers.
As for the pics, the first one appears to be a school photo, the next two look like ID photos. The last two are sketches.
Good thinking, badfreeper. Perhaps some passengers reported they acted suspiciously and they didn't drive over the border by car after all.
Maybe the FBI shaved the "faces" for all intents and purposes?
sw