[Win32] How compare two image

[Member 2965471]

I have to develop an application that captures a portion of the desktop every 30 seconds, after viewing the captured image in the window of application, should find (and then highlight) which regions of the new image have changed compared to the previous image. Ok, so:

HDC memDC;
memDC = CreateCompatibleDC( GetDC(hWnd) );

WM_TIMER:
InvalidateRect(...)

WM_PAINT:
hdc = BeginPaint(...);
screenDC = GetDC(0);

hBmp = CreateCompatibleBitmap(hdc, nWidth, nHeight );
hPrevBmp = SelectObject(memDC,hBmp);

BitBlt(memDC, ..., screenDC, ...);
BitBlt(hdc, ..., memDC, ...);

How can i compare the two image?

[David Crow]

Member 2965471 wrote:

How can i compare the two image?

Read here.

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[Member 2965471]

I've only understand i've to perform a XORing operation between the two image, but how can i do that? and then how can i highlight rectangular region modified? using GetPixel?