An example implementation includes an apparatus including a processor to divide a digital image into a grid including a first grid region and a second grid region. The processor is also to generate a first grid-based watermark using shared watermark information and a first set of grid coordinates associated with the first grid region. The processor is further to generate a second grid-based watermark using the shared watermark information and a second set of grid coordinates associated with the second grid region. The processor is further to embed the first grid-based watermark into a first region of the digital image corresponding to the first grid region and to embed the second grid-based watermark into a second region of the digital image corresponding to the second grid region. The processor is further to generate a machine-readable digital image including the embedded first grid-based watermark and the embedded second grid-based watermark.