Embedded images not displaying in Excel

I'm currently working on an export from actionscript to excel. Images displayed in our flash application are not present on the users on the PC. As a result, I've resorted to imbedding the images in the generated html using the "data:image/png;base64,<base 64 encoded data string>" format.

If I change the extension on the resulting file from XLS to html and open it in a browser I see the images. If I open the .xls file in excel I get the transparent box with the red x.

I'm attaching the generated xls file. Any ideas or recommendations?

Thanks,

Terry