集合视图中的图像在滚动时正在变化

I am working in xcode 8.3. I have a CollectionView. I have downloaded images from web sevice and placed the images in each CollectionView cells. But when i scrolling the CollectionView, images in the each cells are changing. After a few minutes it shows the correct image. I have tried many solutions available in stackoverflow. But i didnt get a solution. Please help me. I am working in xcode 8.3. I have a CollectionV