Sorry, but what you're suggesting is the equivalent of "every airplane should fly flapping its wings" "if the image contains enough signal that a theoretically

Sorry, but what you're suggesting is the equivalent of "every airplane should fly flapping its wings" "if the image contains enough signal that a theoretically optimally trained eye can detect the contraband, they should be able to use machine learning algorithms to detect suspicious items and make them show up with higher contrast." The type of processing which you'd run on an image to make it easy on the human eye is entirely different than what you'd do for ML applications.