Water Sensitive Papers (WSPs) are probably the most widely used artificial targets for assessing spray quality in pesticide applications. However, droplet size and density calculation using WSPs are affected by several factors, being the spread factor and the stains’ overlapping degree the most important ones. Thus, WSPs may present very complex patterns when the percentage of covered surface increases, making difficult the interpretation during the image analysis. Under these circumstances, simulations may help to understand the phenomenon. In this study, WSPs were simulated by varying the percentage of covered surface and recording the number of overlapped stains for each test condition. Simulations were implemented in R software, using the drop size distribution coming from an ATR 80 hollow cone nozzle at a pressure of 1.0 MPa. Drop stains were represented as black circles on white background. Simulated images were treated as real images coming from scanned WSPs and then analyzed using the ImageJ software. Results coming from image analysis were compared to those used for simulations, allowing to relate droplet density, stain density, degree of overlap between stains and percentage of overlapped stains to the percentage of covered surface measured on the WSP images. These data may help to interpret real WSPs used during phytosanitary treatments and to reduce the use of chemicals in plant protection.