A system can comprise a memory to store machine readable instructions and a processing unit to access the memory and execute the machine readable instructions. The machine readable instructions can comprise a feature set extractor to extract a feature set from each of a plurality of digital images of print samples. The feature set can be a filtered feature set that includes a feature set characterizing a printer that printed a given print sample of the print samples. The machine readable instructions can also comprise a cluster component to determine clusters of the print samples based on the feature set of each of the plurality of scanned images of the print samples. The machine readable instructions can further comprise a printer identifier to identify the printer of the print samples based on the clusters of the print samples.