Rather than creating the image dynamically in the code....
Seeing as your creating the html for a table and then adding the image to that...
Why not change your code line from
sb.AppendLine(img.ToString());
to the below instead?
sb.AppendLine("<img src='images/sample_seller.gif' />");
Note:
I had added more but i deleted it because the forum processing is messing up the sample code where when i use double and single quotes in a <pre> block it gets screwed up.