The HTML markup of a web page includes the page's textual content, semantic and styling information, and, typically, several references to external resources. External resources are content that is part of web page, but are separate from the web page's markup - things like images, style sheets, script files, Flash videos, and so on. When a browser requests a web page it starts by downloading its HTML. Next, it scans the downloaded HTML for external resources and starts downloading those.
A page with many external resources usually takes longer to completely load than a page with fewer external resources because there is an overhead associated with downloading each external resource. For starters, each external resource requires the browser to make an HTTP request to retrieve the resource. What's more, browsers have a limit as to how many HTTP requests they will make in parallel. For these reasons, a common technique for improving a page's load time is to consolidate external resources in a way to reduce the number of HTTP requests that must be made by the browser to load the page in its entirety.
This article examines the free and open-source ASP.NET Sprite and Image Optimization Framework, which is a project developed by Microsoft for improving a web page's load time by consolidating images into a sprite or by using inline, base-64 encoded images. In a nutshell, this framework makes it easy to implement practices that will improve the load time for a web page that displays several images. Click here to read the entire article, Optimize Images Using the ASP.NET Sprite and Image Optimization Framework.