A method for performing security screening at a checkpoint is provided. The method includes providing an X-ray imaging system having a scanning area and providing a supporting device for supporting articles to be scanned in the scanning area, wherein the supporting device has at least two reference areas manifesting respective X-ray signatures when exposed to X-rays, the X-ray signatures being distinguishable from one another. The method further includes placing an article to be scanned on the supporting device, introducing the article to be scanned in the scanning area while the article is supported by the supporting device and using the X-ray imaging system for deriving the X-ray signatures of the reference areas and for obtaining an X-ray image of the article while the supporting device is in the scanning area. The method further includes using the X-ray signatures to derive X-ray attenuation information from the X-ray image and using the X-ray attenuation information in determining if the article is a security threat.