We have a C# application that generates Excel files and includes data in the
files based upon the "account" that the user selects. It has worked fine,
but now we want to insert an image (PNG file) into one of the cells. I am
able to create a hyperlink to the picture, but the image itself does not
appear on the Excel file (if I click on the cell it opens a browser window
and displays the image by itself, but it does not appear in the Excel file).
To create the Excel file, we create a large XML string formatted for Excel,
then write it to Excel using System.Web.HttpContext (setting the ContentType
= "application/vnd.ms-excel").