The blank.gif is a 1x1 transparent image file that loads very quickly because of it's tiny size. Then JavaScript code checks if the image is visible on the screen (after page load or page scroll) and replaces the value of the src attribute with the value of the data-src attribute. This triggers the loading of the original image. It's a very simple and powerful implementation, but it has some drawbacks.





One of the them is the lack of responsive images support. Hopefully, this can be easily fixed. The updated version looks like this: