You are right - the AlphaImageLoader filter has been removed from IE9. This has been done so that it does not conflict with methods that are compatible with standards. In this case, pointer-events: none , which now works in IE9 .
If you use conditional comments for the target IE to fix the filter, change them to the target only IE8 and below. Try changing <!--[if IE]> to <!--[if lte IE 8]>
Edit: I already came across this again, and it seems that pointer-events: none does not work in IE9 (and not for HTML elements). I thought this worked, but when re-testing, none of the methods work to transition to IE9. Maybe I had IE9 in compatibility mode.
It is not perfect at all, but you can force IE9 into IE8 using the <meta> :
Apologies for the misinformation, I will continue to study this.
September 24, 2012 update:
The remarkably useful caniuse.com contains additional information about pointer-events for HTML. Support in IE10 is not yet known, and it seems that Opera does not support this property. I would now recommend using pointer-events unless you specifically target Webkit / Mozilla.
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