A common problem that a wordpress.com blogger encounters is of integrating Flickr photostream with the blog posts, since wordpress.com is quite strict in allowing external integrations on blogs. For the same reason, plugins for free blogs are not available for this purpose. Broadly speaking, there are two easiest methods to integrate your flickr photo-sets into the wordpress.com blog posts:
1- The easiest way is to integrate with the help of Flickr’s own slideshow. To do that, first of all, of course, you have to create an account on Flickr and organize your photos into sets. After that, Flicks gives you a slideshow option to display the pictures as a slideshow – clear and elegant. While the slideshow runs, there’s a button "share this" on the right hand corner. Clicking it gives you the HTML code that you can embed in the HTML section of your blog or website and that’s it! Flickr slideshow would be up and running on your blog.
But with ease comes problem. There have been several instances when the above simple way couldn’t work with wordpress.com free blogs, reason again being their strict policy against external integration. So, here is another method, which actually worked for me, to meet the same ends:
2- In this method, you have to use the VodPod extension for Firefox to carry out the task. First of all, following the same instructions as in method 1, get the HTML code for your album from the flickr slideshow’s "share this" button. Then register a free account at Vodpod. After that, create VodPod’s bookmarklet in Firefox’s Bookmarks Toolbar. This would appear as "post to wordpress" in the toolbar. Now every time you have to integrate your flickr slideshow into your wordpress.com blog post, all you need to do is to click on the toolbar option "post to wordpress" and enter the HTML code into the space provided in the link that opens. The post goes directly to your wordpress.com blog.
There are also some third-party extensions for this purpose, but the above two methods are the simplest and most widely used methods for this purpose.