One thing to keep in mind when generating sprites is cachability and the various paths that people will take through your site. You should consider the probability of those sprited images being served together on a page. I've seen people blindly sprite all their images on their site, even if only a small percentage of those images are used on a key landing page. This can cause a bad first impression with a slower experience than necessary. Worse still, I've seen people create a separate sprite for each page on their site and complete lose the benefits of local browser caching. While this might look good on a single WebPageTest, it's terrible for your overall performance. A good method is to identify your top landing pages, then look at which images always appear together and might make sense to be sprited. Keep in mind, if they are small and are included on every page, it may make sense to use a data URI instead. You'll also want to make sure to sprite your images in the same order vertically that they appear on the page to allow for progressive loading.