It looks to me like one of the plastic lens/films sandwiched between the TFT panel + backlighting has somehow become a little skewed.
JB

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Byrd's idea sounds good to me. It's been a while since I took one apart but I think there is a thick semi clear plastic light spreader panel, a thin plastic diffuser sheet, a thin plastic polarizer, then the LCD guts, from back to front. That polarizer sheet needs to be at the correct angle relative to the front bonded polarizer in the LCD to get good extinction (blackness) at all points excluding where the pixel field voltage is playing with the twist of the LC material. Perhaps the plastic sandwich was put together with the polarizer slightly cocked, or even worse if mechanical keying does not prevent, in the correct layer order but reversed front to back so that any angular error is doubled. And it would be really bad if the diffuser and polarizer were order interchanged! If you decide to do some investigation, you can just view each individual sheet with polarized sunglasses on to see which one does the polarization function.