The main purpose of this book is to deals with simple and reliable algorithm for the detection of rain drops size, measure the fall velocity, and measure the drop velocity and also the direction of the drops or rainfall. In this book we are using the images and videos database from Digital single lens-reflex camera (also called digital SLR or DSLR) for detection of raindrops and also measure number of raindrops present in the particular picture frame. The images and videos database used in the book are processed using the Image Processing. Also found the useful information from used database. With the help of background subtraction method and image segmentation method it is possible to find out fall drop size and amount of rain water reaches to the ground. The human approach is neglected in this method, due to which the accuracy of this method is increases. Experimental information also elaborate in this book.