Burn in is not possible with LCD displays.  The term burn in gets its roots from damage to the active area of a cathode ray tube phosphor surface where the electron beam is stationary with high acceleration potential.  This would cause the phosphor to glow very brightly and produce enough heat to signficantly change its fluorescence characteristic.  A fine stationary beam is not a normal picture scenario so severe pinpoint burns are rare.
With the advent of video games and broadcast branding, stationary images often nearly monochromatic with high indexes present a threat to conventional cathode ray and some plasma technologies.  LCD is immune to this.
It is possible for the LCD to show a previous stationary pattern but this is not irreversible like phosphor burn in.  -M