Hello:
Try this (in tcl)
    vtkRenderWindow renWin
       renWin AddRenderer ren1
    vtkWindowToImageFilter renimagen
       renimagen SetInput renWin
    vtkJPEGWriter jpg1
      jpg1 SetInput [renimagen GetOutput]
      jpg1 SetFileName filesalida.jpg
      jpg1 Write
-- 
Jose Luis Pina
jlpina at ivo.cps.unizar.es