Problem with L620 white case cover

[shelzds]

Hi Guys, i bought a Lumia 620 white 3 months before, that time white case was clean with no marks and all, but now i can see some marks inside its case. see the below picture..

what is this marks? :amaze:

 

[xandros9]

I can't really tell from the photo, are those smudges?
I think my sister's 521 case (Incipio, bought online) has a similar issue.

 

[shelzds]

Dont know really what mark is that. i was using a cover so its not any scratches, black line marks are inside its outer cover. damn (