How to get background

Hello:
I use bitblt() copy a bitmap to screen.But I need
the background of bitmap.(it's said all graphic keep up
when bitmap move on it.)
any advice!Thank you!

Is this the question, you have to keep the background while bitblt, try this and let me know

// transfer non-gray pixels to the screen
if (GetDeviceCaps(hdc, CAPS1) & C1_TRANSPARENT){
SetBkMode(hdc, NEWTRANSPARENT); SetBkColor(hdc, RGB(0xc0,0xc0,0xc0));
BitBlt(hdc, x, y, cx, cy, hdcButton, 0, 0, SRCCOPY);}

Hello:
I had test the code.I use VC++6.0 MFC ScrollView
Class.But when I run the code.There are three error
"CAPS1,C1_TRANSPARENT,NEWTRANSPARENT"Undefined.The
code add to mouse Message function.I defined "CDC*
pDC=GetDC()"on top.
I don't know how to do again?Please help me?Thank you
Yoh-Hei