Thoughts that I worship not Allah

It all started with the fact that during prayer and at other times I have terrible thoughts in my head. Namely, I see images of Allah. I realize that I should not do this, but I cannot get rid of these thoughts. I feel that I am committing kufr. Recently, while praying, I had the idiotic thought that I was worshipping my classmate. I quickly told myself that I was only worshipping Allah, however I am afraid that I have indeed committed kufr. What should I do in this situation and have I really committed kufr/shirk?