In an example method, a first dot pattern of shadow dots and second dot pattern of highlight dots is generated. The first dot pattern and second dot pattern include information to be encoded across the image. The first dot pattern and the second dot pattern are mapped to a corresponding subset of the greyscale source pixels, the greyscale source pixels corresponding to an image to be printed. A value of a greyscale pixel in the subset of the greyscale source pixels is modified based on a predetermined threshold pixel value. The value of the greyscale pixel is set to a highlight dot value in response to detecting that the predetermined threshold pixel value is exceeded or set to a shadow dot value in response to detecting that the predetermined threshold value is not exceeded. The image including the subset of pixels with modified values is printed.