UPDATE!

You can find my latest IE PNG hack at ScriptingMagic.com. The latest version does not use HTC, it is pure JavaScript. It also produces faster results because it is configured for specific <img> or <input> tags.

PNG Alpha Hack for IE 5.5+

Add alpha support transparently (no pun intended ;-) to Internet Explorer using behaviors and the standard IMG tag.

To use this hack, you'll need to extract the contents of pngHack.tar.gz or pngHack.zip into the root of your webserver. Then, simply add the following line to any page you would like to support PNG alpha. 

<link rel=stylesheet href="/pngHack/pngHack.css" type="text/css">
Make sure you specify the height and width of the PNG or the image will be automatically sized to 1x1.

Only Internet Explorer will be affected as other browsers will simply ignore the "behavior" CSS property.

Hopefully, this hack won't be necessary in the future.

Please Note:

  • This only works with 32 bit PNGs. 24 bit PNGs contain no alpha info and IE incorrectly displays 8 bit PNGs with alpha.
  • For security reasons IE will not allow behaviors that reside on a different server than the page they are referenced from.

This technique was inspired by http://webfx.eae.net/dhtml/pngbehavior/pngbehavior.html.