In exception, error showing you are converting byte[] to int. Below line of code is throwing this exception Where you are converting
byte[] pa_img =(byte[])Customer_Function.Customer_Operation.Show_Customer_Image(
Convert.ToInt32(this.dataGridView_ShowData.CurrentRow.Cells[0].Value )).Rows[0][0];
Use the following code but not sure what type of Show_Customer_Image() is expecting, Pass your value according to the expected data type, that should be byte[].
byte[] pa_img = (byte[])Customer_Function.Customer_Operation.Show_Customer_Image((byte[])this.dataGridView_ShowData.CurrentRow.Cells[0].Value).Rows[0][0];