Indicates the URL of a lower-resolution (or alternate) image to download into the document space if the image of the src attribute will take a long time to download. The lowsrc image should be the same pixel size as the primary src image. It makes sense to change the lowsrc property only if you are also going to change the src property. In this case, make sure you change the lowsrc property first so that the browser knows how to handle the long download for the src image.