und wieso bekomme ich hier
0,0
0,0 ?

POINT findImageOnScreen(HBITMAP img, HDC screen)
{
	HDC hdcCompatible = CreateCompatibleDC(screen); 
	HBITMAP screenBitmap = CreateCompatibleBitmap(screen, GetDeviceCaps(screen, VERTRES), GetDeviceCaps(screen, HORZRES));
	SelectObject(hdcCompatible, screenBitmap);
	BitBlt(hdcCompatible,0,0,GetDeviceCaps(screen, VERTRES), GetDeviceCaps(screen, HORZRES), screen, 0,0,SRCCOPY) ;

	SIZE bitmapSize;
	GetBitmapDimensionEx(img, &bitmapSize);
	SIZE screenSize;
	GetBitmapDimensionEx(screenBitmap, &screenSize);
	printf("ScreenSize: %i, %i \n", screenSize.cx, screenSize.cy);
	printf("bitmapSize: %i, %i \n", bitmapSize.cx, bitmapSize.cy);
// [...]

?? die bitmap(img) ist vorhanden und wird geladen

The GetBitmapDimensionEx function retrieves the dimensions of a compatible bitmap. The retrieved dimensions must have been set by the SetBitmapDimensionEx function.

Schau dir mal stattdessen GetObject() an!

POINT findImageOnScreen(HBITMAP img, HDC screen)
{
	HDC hdcCompatible = CreateCompatibleDC(screen); 
	HBITMAP screenBitmap = CreateCompatibleBitmap(screen, GetDeviceCaps(screen, VERTRES), GetDeviceCaps(screen, HORZRES));
	SelectObject(hdcCompatible, screenBitmap);
	BitBlt(hdcCompatible,0,0,GetDeviceCaps(screen, VERTRES), GetDeviceCaps(screen, HORZRES), screen, 0,0,SRCCOPY) ;
	HDC hdcImage = CreateCompatibleDC(screen);
	SelectObject(hdcImage,img);
	BITMAP imgInfo;
	GetObject(img, sizeof(BITMAP), (LPSTR)&imgInfo);
	BITMAP screenInfo;
	GetObject(screenBitmap, sizeof(BITMAP), (LPSTR)&screenInfo);
	SIZE bitmapSize;

	bitmapSize.cx = imgInfo.bmWidth;
	bitmapSize.cy = imgInfo.bmHeight;
	SIZE screenSize;
	screenSize.cx = screenInfo.bmWidth;
	screenSize.cy = screenInfo.bmHeight;
	printf("ScreenSize: %i | %i \n", screenSize.cx, screenSize.cy);
	printf("bitmapSize: %i, %i \n", bitmapSize.cx, bitmapSize.cy);
	for(int i = 0; i < screenSize.cx; i++)
		for(int j = 0; j < screenSize.cy; j++)
		{
			if(cc(GetPixel(hdcImage,0,0), GetPixel(screen, i, j)))
			{
				//printf("Fitting entry pixel found @ %i, %i \n", i, j);
				bool found = true;
				for(int k = 0; (k < bitmapSize.cx) & (found == true); k++)
					for(int l = 0; (l < bitmapSize.cy) & (found == true); l++)
						if(!cc(GetPixel(hdcImage,k,l), GetPixel(screen, i+k, j+l)))
							found = false;
				if(found == true)
				{
					POINT ret;
					ret.x = i;
					ret.y = j;
					return ret;
				}
			}
		}
	POINT ret;
	ret.x = -1;
	ret.y = -1;
	return ret;
}

int main(int argc, char* argv[])
{
	HDC hdcScreen = GetDC(0);
	HBITMAP img = loadImg("test.bmp");
	if(!img)
		printf("Image not found \n");
	else
	{
		POINT test = findImageOnScreen(img,hdcScreen);
		printf("found @ %i, %i \n", test.x, test.y);
	}
	return 0;
}

interessant wirds bei
printf("ScreenSize: %i | %i \n", screenSize.cx, screenSize.cy);
denn hier bekomme ich 1024 | 1280 ausgegeben !!
wieso wird da breite und höhe ausgetauscht ?