Oh most webcams you can turn the camera bit itsself...its kind of hard to explain. where the camera lens is theres a dial around it when you turn that it can either to more blury or become sharp depends which way you turn it :)
Sometimes this happens to me, I just restart the computer. But there are some computers where you can have settings for the webcam. If this is yours, you can sharpen the quality.
You can clean it or you can turn it on and off, or go to settings and see if something is making it that way.
sharpen it thru the settings