Command line control of a webcam to capture single images

I would suggest looking at IP camera's.  Its probably far simpler to write a network request for a image than deal with the windows API's.

If you used a network camera from Axis they actually provide a full SDK for free.  The SDK provides full documentation for direct http control and also a activex control that does the work for you.

You can get a basic unit like the 206
http://www.axis.com/products/cam_206/index.htm

here a newegg link with price of $175,
http://www.newegg.com/Product/Product.aspx?Item=N82E16881121009

So not free but its the SDK and hardware for the cost of a decent camera.

Axis is one of the more 'open' companies when it comes to letting you work with the camera for custom applications.

These camera's can also work with a standard FTP server to dump images down.  So you could set the camera to just continually overwite a give jpg file.  Then just copy the current file to your DB or whatever when somebody clocks in or out.  Pretty foolproof to do plus anybody could check in to 'live view' at any time.

you can use a code in VB using the avicap32.dll.

here is the code for connecting a web cam and take a snap shot.
you can add the time stamp to the picture by loading it to an image control and add to it a lable with th time stamp:

Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function capCreateCaptureWindow Lib "avicap32.dll" Alias "capCreateCaptureWindowA" (ByVal lpszWindowName As String, ByVal dwStyle As Long, ByVal X As Long, ByVal Y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hwndParent As Long, ByVal nID As Long) As Long

Private mCapHwnd As Long

Private Const CONNECT As Long = 1034
Private Const DISCONNECT As Long = 1035
Private Const GET_FRAME As Long = 1084
Private Const COPY As Long = 1054
Private Const WM_CAP_SET_VIDEOFORMAT = &H400 + 45


Public Sub wbcStart(hWnd As Long, Optional wX = 0, Optional wY = 0, Optional wWidth = 100, Optional wHeight = 100)
    mCapHwnd = capCreateCaptureWindow("WebcamCapture", 0, wX, wY, wWidth, wHeight, hWnd, 0)
    DoEvents
    SendMessage mCapHwnd, CONNECT, 0, 0
    SendMessage mCapHwnd, WM_CAP_DLG_VIDEOFORMAT, 0, 0
    DoEvents
End Sub

Public Sub wbcStop()
    DoEvents
    SendMessage mCapHwnd, DISCONNECT, 0, 0
    SendMessage mCapHwnd, DISCONNECT, 0, 0
    SendMessage mCapHwnd, DISCONNECT, 0, 0
    DoEvents
End Sub

Public Sub wbcTopPicture(Picbox As PictureBox)
    SendMessage mCapHwnd, GET_FRAME, 0, 0
    SendMessage mCapHwnd, COPY, 0, 0
    Picbox.Picture = Clipboard.GetData
End Sub