This is really unknown issue to many people. I would raise a question for it and make it easily accessible for other, and maybe someone of you know the solution for this problem.
All of us probably know that there is problem with alpha transparency in PNG24 in IE6 (still used by many people on web..). There are at least few known solutions how to solve that, but all of them got their problem that I would like to describe there:
1.Using progid:DXImageTransform.Microsoft.AlphaImageLoader:
This is most common trick to make images shown in IE6. Problem is that it uses DirectX to show it. So basically DX firstly need to download file from Net, then render it. This downloading block browser context for a while. But if you have alot of images - that means that you page can be freezed for even... few minutes (it happens to mine one project at least once).
http://blogs.cozi.com/tech/2008/03/transparent-pngs-can-deadlock-ie6.html http://www.stum.de/2008/12/01/do-not-use-alphaimageloader-to-fix-transparent-pngs-in-ie6/
2.Using VML.
You can also use this workaround. However this has a nasty effect of rendering gray box in background, then a proper image, also causing to download image files twice - this however might be because of bad implementation so need to be checked.
3.Using PNG8.
Just forget about solutions and try use PNG8, if prepared correctly can still be looking good.
If anyone knows any other solution please give answer here!