To post photos from Flickr, you first need to Configure your blog to your Flickr account. When this is done, you can post photos from Flickr using following steps:
When you want a blog a photo, look for the ‘Blog This’ button right above it (you will need to click the photo first, if you are viewing a photostream).
A menu will appear, reading Choose a blog below; select your desired blog.
Complete the post information, including the title (by default, this will be the image’s name) and content (if this is a photoblog, you will most likely leave the content section empty).
Click Post Entry.
Now, you can view your blog to see your latest post – created without ever logging into your WordPress.com dashboard.