private void showData(List<Item> collection)
    {
        gwQuestions.AutoGenerateColumns = false;
        gwQuestions.DataSource = addNotSet(collection);

        foreach (DataGridViewRow row in gwQuestions.Rows)
        {
            DataGridViewImageCell cell = row.Cells[2] as DataGridViewImageCell;
            cell.ValueType = typeof(System.Drawing.Image);
            if (collection[row.Index].Result)
            {
                cell.Value = (System.Drawing.Image)Properties.Resources.Check;
            }
            else
            {
                cell.Value = (System.Drawing.Image)Properties.Resources.Cancel;
            }
        }
    }

dataGridView1.CellFormatting += dataGridView1_CellFormatting;

void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
    if (dataGridView1.Columns[e.ColumnIndex].Name == "ImageColumnName")
    {
        if (collection[e.RowIndex].Result)
        {
            e.Value = (System.Drawing.Image)Properties.Resources.Check;
        }
        else
        {
            e.Value = (System.Drawing.Image)Properties.Resources.Cancel;
        }
    }
}