They (O.R. Tambo) have been using the thermal imaging scanner when you clean RSA Immigration/Passport control at least since our first trip then in 2008. The previous purpose was to scan for Yellow Fever. It has been located at the head of the pass port line where you are "fanned out" to have your passport stamped with the visa.
If you are just transiting JNB and making a direct connection to another county you'd miss it, but if you are staying in RSA to hunt or just over-nighting one of the airport hotels or local B&B/Guesthouse, requiring your passport to be stamped, you've gone through the thermal imager and may not have even noticed.
