To convert a JPEG image to a GIF image in C#, you can use the Image class from the System.Drawing namespace.  

In this code, we first load the JPEG image using the Image.FromFile method. We then create a new Bitmap with the same width and height as the JPEG image, and draw the JPEG image onto the bitmap using the Graphics.DrawImage method. Finally, we save the bitmap as a GIF image using the Bitmap.Save method and specifying the ImageFormat.Gif format.