查看此链接:
http://geekswithblogs. net/dotNETvinz/archive/2009/04/23/uploading-and-storing-images-to-database-in-asp.net.aspx [

Check out this link :
http://geekswithblogs.net/dotNETvinz/archive/2009/04/23/uploading-and-storing-images-to-database-in-asp.net.aspx[^]

you will have to scroll down to the bottom to get to the meaningfull information.
Bottom line is that I see that your parameter definition is wrong:
param[0] = new SqlParameter("@img", SqlDbType.Image, length);