A printing device may include a first print engine to print a first image in a first area of a web substrate and leave blank a second area of the web substrate, a second print engine in series with the first print engine to print a second image on the second area of the web substrate in simplex. The printing device may also include an optical sensor to identify a number of alignment indicators on the web substrate, and a controller to engage the second print engine with the web substrate based on the identification of the alignment indicators by the optical sensor.