OSX Major Graphics Bug
Thank you for providing a picture. Unfortunately, based on the image, I can definitively tell you this is a hardware problem. Specifically, your GPU has failed. 

If you wish to confirm this at home, you can do so by taking a screen shot the next time it occurs. If the distortion appears on your screenshot, then the problem is with your graphics processor and you to get your logic board replaced. If the distortion does not appear on the screenshot, then the issue is with your display and you need to get your display replaced. Either way, it's a hardware issue for which no online troubleshooting or solution exists*

*As a makeshift solution to failing/failed GPUs, many users have resorted to using gfxCardStatus to force the discrete GPU off. 

Best of luck.