Clearing bitmap cache?

Ok, so let’s say I make a Flickr app and i can go through pages and pages of photos. When i go to the next page, the same sprites/bitmaps are used as a form of saving memory. Now, I’ve noticed that all of the images that are retrieved from flickr are being cached in the memory and not cleared–the memory keeps going up and up and up. is there a way to clear them manually? I’m aware of the dispose function, but it doesn’t seem to be doing the trick.