I have found this in the help file:
CaptureFromScreen
So TIECSSource = (iecsScreen, iecsPrimary, iecsForegroundWindow, iecsForegroundWindowClient);
...should be improved:
TIECSSource = (iecsScreen, iecsPrimary, iecsForegroundWindow, iecsForegroundWindowClient, iecsWindowHandle);
procedure CaptureFromScreen(Source: TIECSSource; MouseCursor: TCursor = -1; AHandle: Winapi.Windows.HWND = nil);