Which of the following best summarizes a security measure taken post-9/11?

The introduction of body image scanning technology represents a significant advancement in aviation security measures implemented after the September 11 attacks. This technology enhances screening capabilities by allowing security personnel to identify concealed weapons and explosives more effectively than traditional methods.

Prior to 9/11, the focus of airport security was primarily on detecting metal objects, mainly with the use of metal detectors. The attacks highlighted vulnerabilities in passenger screening and prompted a reevaluation of security protocols. Body image scanning technology, which includes full-body scanners, was developed to provide a more detailed view of a passenger's body and clothing, enabling the identification of non-metallic threats that could be hidden from view.

The other options do not represent advancements in security measures following 9/11. For example, limiting the number of flights would not necessarily enhance security but could negatively impact travel efficiency and economic factors. Increasing the size of personal carry-on items does not align with security enhancements, as restrictions on bag sizes were actually implemented to minimize risk. Similarly, a reduction in the number of security personnel would counteract the objective of strengthening airport security following the 9/11 attacks. Thus, the introduction of body image scanning technology is the most appropriate summary of a key security measure adopted in response to those events.