1. A computer-implemented method to share a region of a screen, comprising: configuring, by a processor unit in a first computer system using a screen sharing tool, a sharing session for sharing the region of the screen with a second computer system, wherein the region is defined by a user of the first computer system to dynamically share a selected portion of the screen by creating a pixel map of the region, and wherein the region is selectively defined using regular, simple shapes, including rectangles or circles, complex irregular shapes of a usable form for selecting a useable region of screen, and a set of regular and irregular shapes, and wherein the region further comprising one or more regions defined on the screen; assessing, by the processor unit in the first computer system, information on performance of the sharing session, including assessing performance of client devices; determining, by the processor unit in the first computer system, from the information on performance a minimum size of the region based on the assessment; and selecting, by the processor unit in the first computer system, the region to share based on the assessment and a designation by the user.