A

Step 1: When the bullet of mass m is fired with speed V, it creates a backward motion of the gun (mass M) due to conservation of momentum. The speed of the gun is given by \( V_g = -\frac{mV}{M} \).

Step 2: The position of the image formed by the concave mirror will appear to be behind the mirror due to its concave nature. The mirror's focal length f determines the location of the image based on the mirror formula: \( \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \), where u is the object distance (which will be negative for the bullet) and v is the image distance (positive).

Step 3: The velocity of the image formed by the mirror will match the speed of the bullet as it changes in time, considering the image is formed in line with the bullet.

Step 4: The speed of separation of the bullet and the image takes into account their velocities moving apart:
\( v_{separation} = V - (-V_g) = V + \frac{mV}{M} = V \left(1 + \frac{m}{M}\right) \).

Therefore, the speed of separation of the bullet and the image just after the gun was fired is \( V \left(1 + \frac{m}{M}\right) \). Thus, the correct answer reflects the motion dynamics after the shot.