The present invention provides an emerging security or authentication feature for objects (e.g., identification documents, product packaging, banknotes, etc.). One method recites: exciting an object with a first non-visible light, the object comprising first indicia provided with a first ink or dye and second indicia provided with a second ink or dye, the second ink or dye comprising an emission decay time that is relatively longer than an emission decay time of the first ink or dye, the first indicia and the second indicia collectively conveying a first machine readable feature when illuminated with the first non-visible light, with the second indicia individually conveying a second machine readable feature after emissions attributable to the first indicia fall to a first level; and machine detecting at least the second machine readable feature after emissions attributable to the first ink or dye fall to the first level and before emissions attributable to the second ink or dye fall to a second level. Other combinations are provided as well.