After a certain period of time the photos in my photostream won't load properly

When I try to open a photo from a few months ago, per example, a circle shows in the down right corner of the screen and shows that the photo is loading. Anyway, it doesn't load at all and if I try to use the photo for something, they say its 'downloading'. My question is, what can I do to the photos or maybe should I move them to a computer or something so I can actually have them in a nice quality. I guess the problem is related to iCloud.