Images sometimes does not show in the subtotal section when export to Excel. This article demonstrates one working example on how to apply image in threshold and make sure it will display in subtotal section in Excel.
1) Image reference. The recommend image reference is to use HTTP reference other than relative/absolute directory. In this way the image is accessible from one or more client machine when exporting to Excel. One test user can do is the Strategy logo image provided on Strategy.com
http://www.microstrategy.com/graphics/homepage/homepage_logo.gif
2) When reference the image, make sure to use the "Advanced Threshold Editor" on Web and choose "apply on both metric and subtotal" to make sure that the image displays on both location. See screenshot below:
3) Check "embed image as picture" in the export options. The image should display in exported Excel book on both grid and subtotal section:
