I have looked through all of your tutorials but haven't seen anything on how to crop an 8-bit image so all of the black part is removed. I am trying to crop an 8-bit bmp image to the bounding rectangle.
I'm not sure I totally understand what you are trying to do..
What I think you need is Alpha Testing. Take a look at lesson 32
Alpha testing uses the alpha channel to make parts of an image translucent, obviously an 8 bit BMP won't have an alpha channel but you can generate one using the source by assuming any non-black texel has an alpha of 1, and any black part has an alpha of zero.