That without a doubt looks like 3D vision is enabled, as pointed out by Toveri.
If you haven't enabled this in-game (I don't know if LoL has that feature), make sure it's not forced in your GPU drivers. For Nvidia you have separate drivers for 3D Vision, which you can un-install via "Add or remove programs", if you don't need it.
When you install or re-install new Nvidia drivers "Nvidia 3d Vision Drivers" is ticked by default.