Need advise with making USB LED string Answered

Hey all, First post and I have an itching to make something for once, I want to make an "Infinite Mirror", I have seen a few instructables on how to proceed, My main concern is that most of them are battery operated, And I want to operate mine from USB, Now I will put 12 lights in a string, Then output to USB , But will I need any resistors, chips ect? or will just wiring up 12 LED's straight onto a USB end work? I don't want them to do anything fancy, Just be on when plugged in. Any help would be greatly appreciated. 

Thank you!