C# .jpg help pls

Can i get some help?
I am making a program in c# that hides strings into images by changing each pixel color to be odd or even so i can store binary data in the pixels without changing the over all look of the image. Its just something i am making for fun but it only seems to work with .bmp's. I want to get it working with .jpg but i dont know how to do this. Right now i am just using System.Drawing.Bitmap to modify the images. Is their any other way that i can do this so it will be compatible with .jpg?

>>1
This idea is rather stupid. For a start not all image formats use pixels, and you could just put the string straight in to the file somewhere (most likely an extension area) with a reasonable understanding of image specification.

>>6
The JPEG specification specifies both lossy and lossless methods of compression. On top of that, nobody said he is making his changes before compression- if you read in to it you could probably figure out some way to get your bits of information stored in what will become the decoded DCT matrix.