Well, I've seen some strange display issues your's takes the cake!
Somehow the displays cell's broke down, this is were the Thin Film Transistor (TFT) within the LCD has failed. Whats weird here is the grouping of the failed cells is so scattered. Did something hit your display at some point? It could have been a while ago. This damage is within the sandwich of the LCD so you can't fix it.
Here's a bit more on your display technology: Thin-film transistor liquid-crystal display
Sadly you'll need to replace your display assembly to fix this. Here's the IFIXIT guide: MacBook Pro 15" Unibody Early 2011 Display Replacement and here's the needed part: MacBook Pro 15" Unibody (Early 2011-Late 2011) Display Assembly