It has already been proven that things can get pass the TSA screeners who are viewing the images and it may not have anything to do with training. It may be simply because they yawned, sneezed or looked away from the monitor screen for a second. Impossible to stop a TSA screener from doing those things. The only way to solve that problem is to make the NOS/WBI read the image itself and find the suspicious items, but that isn't full proof either since a machine can also miss something due to mechanical failures. So really the TSA screener or the NOS/WBI neither one is all that effective since they both can let dangerous items get pass them and onto the plane.