Hi!
A couple a days ago, I started to have this kinda of image.
Sometimes it wont happen, sometimes it screws my display, all kind of picures.. images etc. Everytime I took a screen shoot, all I got is a black screen.
Should I take it to a repair center?
I would certainly take it in to be looked at. Even though restarting it fixed it, you should definitely have it checked. I'm a firm believer in "better safe than sorry" as much as these machines cost. Even if everyone tells you that a problem is no cause for concern (which this one surely is!) if you, the purchaser, are uncomfortable with your product, take it to Apple and ask them about it. They are very accessible, and that's what they are there for and what your warranty is there for