Flickr has an amazing wealth of personal and professional photos available for viewing and copying. When copying a Flickr photo, you are downloading it, which means you copied it from the website to your computer. Not all photos can be downloaded, since users may elect to keep their photos private. Circumventing such settings may be illegal, and should not be attempted. There are still a massive amount of photos on Flickr that you are legally allowed to download.
Search for photos you are interested in by entering keywords in the "Search" field on the Flickr home page.
Click the photo that interests you.
Click the "Actions" menu above the image and choose "View all sizes."
Click the image resolution that you want from the horizontal list, and click "Download..." to download the photo. If the download option is not present, then the photographer does not allow copying of her photo.
Click the "Request to license" link near the image from the photo page, if you'd like to use the photo somewhere else. Not all users have this feature enabled, but for those that do, it will enable you to negotiate the download and use of the photo on other websites or publications.