Flickr2Frame is a free software that lets you download photos from Flickr directly to Digital Photo Frame. Whenever you connect your digital photo frame to your computer, Flickr2Frame will download your photos from Flickr, and will copy them to your Digital Photo Frame.
You can specify your photo sets that Flickr2Frame to should try to download on your digital frame. Flickr2Frame has been very well developed to make it extremely simple to use. I just love the fact that I can directly download my Flickr photos to my digital frame, without a need to separately download them to my computer first.
If your photos are not sized properly according to your frame, you can use JPEG Thumb Maker that batch converts pictures to fit digital photo frame. If you want to bulk download Flickr photos to your desktop, you can use FlickrEdit.
Flickr2Frame is quite easy to use once you have set it up, but the setup can be a bit tricky. However, developer of Flickr2Frame has created a fantastic user guide that guides you through the configuration process. This user guide also explains how you can get API key from Flickr that you will need for Flickr2Frame.