Temporary bitmap

I need to make a temporary bitmap of a selected area of my main form. The selected area will be hard-coded as it will not change, but I am uncertain how to create the bitmap without using Bitmap.Save(). This is required to check for pattern alignment between the image on the form and various saved images in a special directory (also to be hard-coded). If I have not been specific enough please let me know. I cannot provide code in this area as I am not sure where to start.