Originally Posted by
Mabuk dan gila
I have on any number of occasions wandered across the San Ysidro-Tijuana border on foot where there is no kind of immigration control whatsoever departing the US or entering Mexico, hailed a cab to TIJ, and boarded flights to both South American countries via MEX or Asia via AM's nonstop TIJ-NRT flight. I've gone as far as Indonesia that way. Prior to WHTI being enforced, I reentered the US on foot using my California Drivers licence as ID. Even that they rarely scanned into the computer and just waved me past leaving no record whatsoever I ever set foot out of the US. Post WHTI enforcement they scan my passport or passport card but still have no record of when I left on foot and generally just presume I merely made a day trip barhopping or shopping in TJ like 99.99% of all the other American citizens returning on foot from Tijuana at that border crossing. If they specifically ask me I will honestly answer where I have been but the most questing I ever get is "what were you doing in Mexico" and I answer truthfully "going to visit friends" (I never see that they asked me WHERE was I going from Mexico, or where my friends were, only WHY I was in Mexico. I was in Mexico to GO to visit friends).
The thread is primarily discussing inspection and passport scan by a CBP when entering the country. What I wrote pertained to air travel or travel by scheduled operators. I never made any claim that DHS knows that you have departed by every possible means. Sorry, but I don't see the relevance of your post to the thread. If you go back far enough, you could enter the country even without a passport. There weren't even any passports at one time. What happens at a border without immigration control is also not relevant to the question posed by the OP. Operator of any flight that flies to over U.S. territory is covered by APIS too. You might think no one knows but DHS might know, when you walk across the border and take an AM flight to MAD.
While your post is interesting it does not shed light on the issue posed by the OP.