Image segmentation is important consideration in computer vision. Image segmentation partitions the image into multiple regions. For image segmentation, a number of different methods have been available in the literature. In this book, Ostu Threholding and Watershed Method have been described. In Ostu Method, the image is segmented at different values of threshold and some interesting points have been found. Watershed has also applied on the same image for segmentation. The performance of these methods have been tested using seven well-known performance measures. The effect of image size has also been analyzed on both methods. The analysis of these methods is beneficial for research community.