When you use a DataGridViewImage column within a DataGridView, a red "x" will show up if you do not anything bound to the row in question. What this means is that if you have an edit row at the end, it will show the red "x". Unfortunately, neither the official documentation for DataGridViewImageColumn in MSDN nor the forum are very clear on this. I gleaned off one of the last posts which recommended creating a new blank bitmap. Instead, I set my cell value to the value of the image I already set up in designer. For a DataGridView that is not getting databound, you will need to put this in the form load.
private void myGrid_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
//assumes that image column is first column
myGrid.Rows[myGrid.Rows.Count - 1].Cells.Value =