The size of a datagridview cell is determined by the column Width and row Height. Therefore in order to change the cell's size, you must change the cells column width, and the cells row height.
Image image = Image.FromFile("something.png")
int width = image.Width;
int height = image.Height;
int rowIndex = 0;
DataGridViewCell cell = dataGridView1.Rows[rowIndex].Cells["images"];
cell.Value = image;
dataGridView1.Rows[cell.RowIndex].Height = image.Height;
dataGridView1.Columns["images"].Width = image.Width;