Then click on the collection and then the set to find the photo. There are also links from my articles direct to featured photos.
After you've opened the set click on the photo you want. Then click on the little magnifine glass (+) just above the right side of the photo. This takes you to a larger view and then in the upper right you will see a "View all sizes" link. (Note: You need to be logged into flickr to see these links - flickr accounts are free)
The View all sizes link brings you to a page where you can click on various size links from Square (75 x 75) all the way up to Original. Click on the size you want and then click on the link to download that size and save to your desktop or your pictures folder.
If the picture you want is needed in a high-quality .tiff un-compressed format e-mail me and I can make it available to you at not cost for personal use.