有关C#数据库问题

比如 if（数据库中存在图片）//这个条件不懂得怎么写
{
try
{
SqlConnection conn = new SqlConnection("Data Source=(Local);Integrated Security=SSPI;DataBase=StudentManage");//连接字符串
conn.Open();
string sqlstr = string.Format("select StuPhoto from tabStudent where StuNo='{0}'", dgvStu.CurrentCell.Value);
{
SqlCommand mycmd = new SqlCommand(sqlstr, conn);
SqlDataReader myread;
myread = mycmd.ExecuteReader();
if (myread.Read())
{
lblPhoto.Text = "该生照片：";
byte[] mydata = ((byte[])myread["StuPhoto"]);
MemoryStream myStream = new MemoryStream(mydata);
Image myImage = Image.FromStream(myStream);