Until today I didn't know that the App_Data folder cannot contain images. Well, actually it
can, it's just that the images won't be served, for security reasons. Normally I wouldn't put my images in the App_Data folder but rather in a Images folder beneath the root, but I was just testing something today and trying to add an image to a treeview node i put it in the App_Data foder just because the folder
was already there. And then I spent the next 10 minutes trying to figure out why the image wouldn't display. Anyway, you can find more details about this
here.