alt
text is NOT shown on mouse over. And even when shown by non-compliant browsers, the alt
should be describing what is missing, not some tag line. So maybe it should be labeled "The text used on browsers that don't support images" (like by readers used by visually impaired). If a mouse over is wanted too, then besides the alt
attribute, the title
should be specified as well, after the image or link URL. Like: [1]: http://image-url "Tagline to show on mouseover"