That depends on the type of bmp file you are reading.... firstly, you need to retrieve the header info;

In the header info, you have things like the height and width of the image, the bit depth (eg 8, 16, 24 bit).

These links may help:

http://www.fortunecity.com/skyscrape.../bmpffrmt.html

http://astronomy.swin.edu.au/~pbourke/dataformats/bmp/

http://www.cs.uvm.edu/~erickson/educ...b_bmp/BMP.html <-- Create an image in vb)