I too had this problem with my 5s. I think it was giving me headaches. Finally, after convincing myself I wasn't seeing things, I found this thread, and pulled out a 4s and 5 and checked the sample image on it. No flicker.
I went into an Apple store this weekend to get a replacement. I checked the image on a few phones on display, and they exhibited no flicker. Of course the genius tried to convince me this was a normal refresh, caused by the image, to which my demonstration of the iphone 5, and 4s, and then the 5s units they had out, abated such talk. They replaced my phone, but it was still evident.
Today I loaded the beta of 7.1 and the image no longer flickers and I do not yet see the scan lines as described before. Time will tell, but I am hopeful.
Be curious to see if others with access to 7.1 see a similar correction.