Medical use of the thermal cameras and the imagers have experienced significantly gain in the last two decades. Although thermograms with a high spatial and an acceptable temperature resolution would be sufficient for most clinical applications, there are increasing requirements for quantitative analysis of the medical thermograms to facilitate cross-centre data exchange and as an aid to more reliable diagnosis. Therefore, absolute and International Temperature Scale (ITS-90) traceable temperature calibrations of the thermal imagers are necessary. On the other hand, such calibrations are useful to trace the long and short time stabilities of the thermal cameras. This study describes a large area triple point of water cell based blackbody (TPWBB) developed for the traceable and absolute calibrations of the thermal imagers. The results of the measurement campaign for the characterization of the base parameters of the TPWBB are presented. The traceability of calibrations is validated by means of ITS-90 traceable low temperature radiation thermometer with a working bandwidth of 8-14 mu m.