Plant drought stress basically originated from the water shortage, which could be caused by the extreme weather conditions and/or by the insufficient amount of soil water within the rooting zone. The early and exact recognition of drought stress of crops is difficult as no universal drought estimation method can be defined through the complexity of the problem. Side projected canopy images can be used for such purposes in case of different plants as tomato, cucumber, and paprika. The images can be taken to analyze leaf and stem movements as the visual signs of plant drought state. Algorithms developed for using side projected canopy images can also be used for automatic irrigation of greenhouse crops.