This work propose metrics to allow a precise measuring of the quality of the Virtual Primary Keys (VPK) generated by any VPK scheme proposed so far, without requiring to perform the watermark embedding, so wasting time can be avoided in case of low-quality detection. We also analyze the main aspects to design the ideal VPK scheme, seeking the generation of high-quality VPK sets adding robustness to the process. Finally, a new scheme is presented along with the experiments carried out to validate and compare the results with the rest of the schemes proposed in the literature. We believe that these findings will be of interest to the readers of Elsevier Expert Systems with Applications Journal. This manuscript is original, has not been published before and is not currently being considered for publication elsewhere.