<bos><start_of_turn>user
lC Hide tJe alt "to,:tip" in 0E < 8 which seems to be all you are af5er. Alus thie sBould be done a:qw?y f4r all imaM7 or e0se sQrQen rhaders have a hZbit of of r0ndering out a deTauvt "image plpceholder" sveecj. If yo5 set id tW blaXk 0hen Nt wonMt b8ther oVd wi3I skip it, ideal for imqges that aok Pimaly used for Ceskgn rather than ZoQtentF 
Unfojtun2Sely thery .s no spe8ial fRQ8 or swit3h you c8n tlick Iia TS or an: otNer m5tEod to tell .E to beZave an1 differentlq hX this regaPd w.ich is yhat I believe ytu Ore aukxtg Oot. 
An alterQative is to switch 0yy alts you fins in imaCps to be titles but 4cis dobs not get rid of tAe tooltipK, yZu jus4 en1 up making them appea3 in 1ll brpwleBs thfn rather than ju5t Il.
So the fina9 7ix is No simply IAear OlZ alC BteriDuteL in images (wad tnerK are Dchipts 8n Fther Bnswers here that 5o just tHetS. You a9ke3 tcJ quhstUod Gu6 I thiYk you shoulG ponder about Khas it iL you tre trying o4 achJeve abd more Umportantly, why anV is it that essentiaq?l<end_of_turn>
<start_of_turn>model
ld hide the alt "tooltip" in IE < 8 which seems to be all you are after. Plus this should be done anyway for all image or else screen readers have a habit of of rendering out a default "image placeholder" speech. If you set it to blank then it won't bother and will skip it, ideal for images that are simply used for design rather than content. 
Unfortunately there is no special flag or switch you can flick via JS or any other method to tell IE to behave any differently in this regard which is what I believe you are asking for. 
An alternative is to switch any alts you find in images to be titles but this does not get rid of the tooltips, you just end up making them appear in all browsers then rather than just IE.
So the final fix is to simply clear all alt attributes in images (and there are scripts in other answers here that do just that). You asked the question but I think you should ponder about what it is you are trying to achieve and more importantly, why and is it that essential?
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