#include <windows.h>
#include <vfw.h>

#define capSendMessage(hWnd, uMsg, wParm, lParam) ((IsWindow(hWnd)) ? SendMessage(hWnd, uMsg, (WPARAM)(wParm), (LPARAM)(lParam)) : 0)
int capWebCam(char *szFile, int nIndex, int nX, int nY)
{
    HWND hWndCap = capCreateCaptureWindow("CapWebCam", WS_CHILD, 0, 0, nX, nY, GetDesktopWindow(), 0);
    if(!hWndCap) return FALSE;

    if(!capSendMessage(hWndCap, WM_CAP_DRIVER_CONNECT, nIndex, 0)){
        DestroyWindow(hWndCap); return FALSE;    
    }

    CAPDRIVERCAPS capDriverCaps;
    memset(&capDriverCaps, 0, sizeof(CAPDRIVERCAPS));
    capSendMessage(hWndCap, WM_CAP_DRIVER_GET_CAPS, sizeof(CAPDRIVERCAPS), &capDriverCaps);
    if(!capDriverCaps.fCaptureInitialized){
        DestroyWindow(hWndCap); return FALSE;
    }

    capSendMessage(hWndCap, WM_CAP_SET_SCALE, TRUE, 0);
    capSendMessage(hWndCap, WM_CAP_GRAB_FRAME_NOSTOP, 0, 0);
    capSendMessage(hWndCap, WM_CAP_FILE_SAVEDIB, 0, szFile);
    capSendMessage(hWndCap, WM_CAP_DRIVER_DISCONNECT, 0, 0);
    DestroyWindow(hWndCap);

    return TRUE;
}

Aufruf:

if(capWebCam("webcam.bmp", 1, 320, 240)){
        MessageBox(HWND_DESKTOP, "Success", "", MB_OK);
    }else{
        MessageBox(HWND_DESKTOP, "Failed", "", MB_OK);
    }

Ansonsten:
Index durchprobieren und Namen mit capDriverGetName() besorgen.

Die Capture-Programme die ich kenne, verwenden allerdings allesamt kein Vfw sondern DirectShow.