Not to be taken as an answer, just a summary of the above plus a few observations. +1 to everyone, including OP for a very interesting question.
This depends very much on circumstances and OP is not quite clear. Is he swallowing the card when the security forces have nabbed him, or when they look like they might and he has a few minutes time to do something?
It also depends on the technical sophistication of said security forces and that might vary on a case by case basis.
- If the “arresting officers are shown the photos on the camera and they seem innocuous, will they let you go? And how much do you trust that given the possible consequences. One could imagine switching cards, or formatting and saying that one had not yet begun to photograph, but ..
- will the boys back at the station be smart enough to unformat/undelete?
You could auto-upload by wifi – what are the chances of that being monitored? Probably slim, but is it worth the risk? Only the OP can know the possible consequences. Even if the camera would auto-delete after update, can the lab guys undelete? If it’s not auto can you be sure that you will remember to manually undelete each time? And can the lab boys undelete it?
Do any DSLRs offer in-camera file encryption? is probably answered “no”, but even if it were yes, would it be recognized as encryption and the password beaten out of you?
Switching cards and secreting the original, especially a micro-SD, seems like a good idea. Where to secrete? I really liked the idea of slitting the hardened skin on the sole of the foot – very 007. Up the nostril, inside the cheek, in your ear (in your rear ;-), (hmm, read the Choirboys, where the bookie’s runner keeps bets on small slips of paper under his foreskin). Under a plaster, slit the top of your belt slightly and lisp in there?
And, if it does come down to swallowing – follow the advice given and try it now (but remember that “they” might induce vomiting or administer laxatives.
A fascinating intellectual exercise and I am grateful that my liberty does not depend upon the result.