Image processing methods facilitating investigation in laboratory conditions are competitive with respect to traditional methods. In the vast majority of cases these methods make it possible to obtain more accurate results, while at the same time reducing the amount of work and time required to carry out the research. The laboratory tests which are the basis for this paper were connected with researches over the effectiveness of active substances against snails. The tests where made with use of the leaf discs. Slugs feeding preferences were tested in individual compartments with three leaf discs with same size. After a day of feeding the measurement of the damaged surface of leaf discs was made with utilization of millimeter paper. The more precise and considerably quicker method is proposed in this paper the technique of the image acquisition of the oilseed rape leaf discs with flat scanner or digital camera and their analysis in produced application. The image analysis with use of FotoDetekt application markedly simplified the process and provided high-quality measurements.