Methods, computers, and computer program products for detecting the presence of a probe within a sample overlayed on a substrate are provided. The probe comprises a plurality of spatially arranged labels. A data storage module stores a plurality of light images, where each light image has light from the sample at a corresponding wavelength range in a plurality of different wavelength ranges. A label identification module identifies a plurality of labels in the plurality of light images that are proximate to each other on the substrate. A spatial order of the plurality of labels determines a string sequence of the plurality of labels. A probe identification module determines whether the string sequence of the plurality of labels comprises a valid reporter sequence.