There's been understandable consternation with Flickr that when images are downloaded from the site, they're stripped of their metadata. Any information attached to an image, from camera and lens type and geographical location to creator's name and additional copyright information is wiped away. For photographers who are doing their best to keep track of their images and prevent their unauthorised use, or just maintain their integrity while being able to show them off to the widest possible audience, this is more than a little galling. Flickr has listened to at least some of these concerns and from now on, the copyright field in an image's EXIF data will be preserved, for both original and resized image files. For the moment, this is only going to apply to new uploads but there is every intention to retro-fit this piece of data preservation to all uploaded (and then downloaded) images.
It's always worth noting that it is possible to restrict who has access to your original image files on Flickr, and thereby who has the ability to officially download them. (Any image on the Internet can be downloaded if you want it badly enough, hence 'officially'.) You'll find these permissions under Settings > Privacy and Permissions > Who can access your original image files?
Only the copyright line is preserved, nothing else, but at least it's a start. Full details are on the Flickr Forum.