for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{

   int itemid = Convert.ToInt32(ds.Tables[0].Rows[i][3]);
   img.ImageUrl = "~/Handler1.ashx?id=" + itemid;
   img.DataBind();
}

原因是您要遍历数据集中的所有行，然后每次将imageUrl设置为最后一行.您真正要问自己的是，如果一行上只有1张图片，为什么要使用循环?

The reason is that you are looping through all the rows in a the dataset, and then setting the imageUrl to the last one every time. What you really need to ask yourself is Why are you using a loop if you only have 1 image on the row?