How can I make one btimap from 2 bitmap?

I want to clip a region from a Bitmap from centre and bitmap is larger than the monitor scale around 2000*2000 pixles.
How can I cut the region from a bitmap and save that region as different bitmap.
Also i want to make the frame of the bitmap and this bitmap also may be the same size as above and I want to draw the black frame on the bitmap and
save that bitmap with a different name. for this I thought that I can make a black bitmap so I can copy the required bitmap into the black bitmap
in centere. Its not need required to diplay the bitmap on screen. I just want to do it by getting the bitmap patth.