Tento kus kódu se může hodit. Zkusil jsem to.
byte[] imagedata = (byte [])dataGridView1[4, dataGridView1.SelectedRows[0].Index].Value;
using (System.IO.MemoryStream ms = new System.IO.MemoryStream(imagedata, 0, imagedata.Length))
{
ms.Write(imagedata, 0, imagedata.Length);
//Set image variable value using memory stream.
image = Image.FromStream(ms, true );
}