How Should I Use Flickr?

After I uploaded a picture to flickr and wanted to post it in my blog, I found the flowing tips:

Remember! Flickr Community Guidelines specify that if you post a Flickr photo on an external website, the photo must link back to its photo page. (So, use Option 1.)

Flickr provides two kinds of HTML code. The first links to flickr page, like this:

The second is the URL of the picture, like this:
http://farm4.static.flickr.com/3209/3133269506_6d6c83b9ac_m.jpg

The flickr guidelines tell us that we must provide a link from each photo or video back to its page on Flickr. So I think the second code is not allowed. But why flickr provides it?

I used to link the full size picture's URL and show the small size picture in my blog. So visitors can get the original picture directly. Like this:


Up to now, it has no problem. But I'm not sure. Can anyone tell me that can I use flickr like this?