Created around October 2011
Single Pixel Gif as a base 64 encoded string
Single pixel GIF files were a technique to create blocks on a web page which were assured to take up space. In the modern CSS era there is less call for using transparent GIFs like this. A data-encoded image is one which has been encoded such that they are valid image data but don't require a network call.
<img alt="" src="data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==" />