Examining Threat Image Projection Artifacts and Related Issues: A Rating Study
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Threat image projection (TIP) is a widely used software function of X-ray machines at airport security checkpoints. TIP projects fictional threat images (FTIs) of actual pre-recorded threat items (mainly guns, knives and improvised explosive devices) into the X-ray images of passenger baggage before they are displayed to security officers (screeners) for screening. TIP increases attention and motivation of screeners and is often used to measure their detection performance. In order to be effective, TIP has to project FTIs in a realistic way. In other words, it should not be possible to detect FTIs by simply detecting visual artifacts resulting from TIP projection. This study was conducted to evaluate TIP quality regarding potential artifacts. First, we interviewed screeners to explore which TIP artifacts they encounter in their day-to-day work. In a second step, we conducted a rating study to quantify the identified artifacts and the quality of TIP images in general. The majority of images (80%) produced by TIP were judged by screeners to appear realistic. However, in some images FTIs were positioned inadequately: the alignment (compared to the surrounding baggage items) appeared artificial (15%) or the placement appeared physically implausible (17%; e.g. an improvised explosive device going through a heel). These two issues also significantly affected the image to appear unrealistic in general. We conclude that in most cases, TIP succeeds in projecting FTIs without creating discernable artifacts. In some cases however, the FTI is positioned inadequately, which could be improved in the future.