Flickr2Commons is a tool that allows the transfer of images from Flickr to Wikimedia Commons. It can process individual images, sets, or all images by a user. The tool will enforce that only images under acceptable licenses. You need to authorize the tool via OAuth first.
For the current version, to upload a single image, use the Flickr ID number, found in the Flickr photo's URL. For example,
http://www.flickr.com/photos/52614599@N00/4638269682/ has the Flickr ID 4638269682.