Knowledge of the quantity of disease is particularly important to decision-makers in Plant breeding program. Quantifying disease on plants by measuring symptoms falls under "remote sensing". Remote sensing is obtaining information about an object without having direct physical contact with it. Digital image quantifying techniques methods are used to quantify the severity of a given disease. In assessment of plant disease severity, the use of various error terms and how these should conform to current approaches used in measurement science include: Reliability, Accuracy of estimates and Agreement Visual rating methods are, continue to be the single most important way of assessing plant disease for the foreseeable future. The various kinds of scales used in visual plant disease assessment include: Nominal or Descriptive Scales, Ordinal Scales, Ratio Scales, and Interval or Category Scales. Digital cameras are an inexpensive and widely used resource, and used for various applications in plant pathology. A Portable Application for Quantifying Plant Disease Severity. Leaf Doctor is a new tool for the semiautomatic assessment of disease severity for individual leaves or other sampling units. Advantages of digital photography and image analysis in the visible spectrum Image analysis can be quick, accurate and reliable when automated. For disease severity, various statistical methods have been used to explore the quality of image analysis measurements compared with true and estimated values, as well as the repeatability and reproducibility of various methods.