There are a lot of viewers available in the QB world, some being faster than the others.
I found it easier to learn first how to write a .BMP. Displaying them is another story: the size of the pic can be greater than the screen, and, most of all, you can generate fairly easily a 24bits .BMP (i.e. a photographic quality image) with QB, while displaying them is really a "complex" issue.
There are basically 3 types of BMP:
1) the poor formats (monochrome for example)
2) the palet based bitmaps (16 or 256 colours, knowing the 256 colours format can handle the 16 colours)
3) the 24 bits format, which is in fact the easiest to understand, since it has no palet.
Beside these BMP considerations, I can only recommend the following URL:
http://www.myfileformats.com/
You will find there everything you need about the various formats specs (bmp, pcx, gif, etc...)