The momentum distribution of the atomic ions resulting from the Coulomb explosion (CE) of a molecule contains a lot of information about the structure of the molecule just before its CE. A simple imaging formula inverting the momentum distribution into the squared nuclear wavefunction is important in order to deduce the shape of the nuclear wavefunction of the molecule just before the CE. Here simple classical imaging formulae for linear triatomic molecules are presented: a one-dimensional formula for symmetric CEs and a two-dimensional one in terms of hyperspherical coordinates for non-symmetric CEs. We concentrate on imaging a vibrational eigen state of a bound electronic state in this paper. Since the formulae are classical, there appear deviations between the original wavefunction and the inverted image due to quantum effects. It is shown numerically that the quantum effects are predominant around the symmetric geometry when either a symmetric and/or an anti-symmetric vibrational mode is highly excited and the charge state of the atomic ions is low. It is further shown that hyperspherical coordinates are natural coordinates for describing non-symmetric CE imaging. The present wavefunction reconstruction methodology should be applicable to CE by ultrashort laser pulses where ionization occurs much more rapidly than nuclear motion and to highly charged symmetric systems where bending is expected to be negligible.