If you mean convert your string to some image with that string on it ,it would be like this >>
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing.Text;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
using System.Drawing.Imaging;
string textPrntMag1 = "Shivanand";
string textPrntMag2 = "Nagarabetta";
string textPrntMag3 = "All is well";
string textPrntMag4 = "R u usman_k";
Bitmap bitmap = new Bitmap(1, 1);
Font font = new Font("Arial", 15, FontStyle.Bold, GraphicsUnit.Pixel);
Graphics graphics = Graphics.FromImage(bitmap);
int width = 220;
int height = 150;
bitmap = new Bitmap(bitmap, new Size(width, height));
graphics = Graphics.FromImage(bitmap);
graphics.Clear(Color.White);
graphics.SmoothingMode = SmoothingMode.AntiAlias;
graphics.TextRenderingHint = TextRenderingHint.AntiAlias;
graphics.DrawString(textPrntMag1, font, new SolidBrush(Color.FromArgb(255, 0, 0)), 0, 20);
graphics.DrawString(textPrntMag4, font, new SolidBrush(Color.FromArgb(255, 0, 0)), 0, 40);
graphics.DrawString(textPrntMag2, font, new SolidBrush(Color.FromArgb(255, 0, 0)), 0, 60);
graphics.DrawString(textPrntMag3, font, new SolidBrush(Color.FromArgb(255, 0, 0)), 0, 90);
graphics.Flush();
graphics.Dispose();
string fileName = Path.GetFileNameWithoutExtension(Path.GetRandomFileName()) + ".jpg";
bitmap.Save(Server.MapPath("~/images/ShipmentOrders/") + fileName, ImageFormat.Jpeg);
If you mean an image from Base64 encoding:
Convert Image to Base64 String and Base64 String to Image
Or you can see this
post.