Alt text for images

if you just fill out alt text for an image, you do not get the yellow box pop up when viewing website and I am sure below has something to do with it. The alt text tag is good for search engines, does anyone know if this is just as good with out the pop up showing for search engine friendiness?..I actually prefer it visually without

"ExportEmptyTitles - disables the tweak that forces IE to not show a tool tip with the alt property. In case there's no title property we now add an empty one by default. Disabling this registry setting will export the old way.
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Is this one of John Horn (covoxer)'s tweaks.

I think the Alt text will still show up for the benefit of search engines. Publish the page locally, to a folder or the desktop, then look at the Page Source, or Source Code (same thing) and see if you can see the Alt text. If you can then the tweak is probably a good thing and is doing what it is intended to do.

FYI - the "alt" text is displayed when for some reason the image can't be displayed. It is also read by screen readers for the visually impaired. The yellow box displays the "title" text for the image...