I solved this problem by myself.
I imprort png and jpg images and can't check every product to see extension of it's images. So I make formula to have link with png and jpg images when I import products with CSV import.
For example: If I have png image and I set first link to image storage as png, I get cover images. But, if jpg image, I don't. So, first import image must be on server images storage to get cover image.