electricia1 posted in the Community support forums that flickr has changed the way images can be embedded. At the moment this is done with an iframe, which of course is a “no-go” for WordPress.com users.
However, there are other ways you can embed your flickr photos in your WordPress.com site, the easiest is still just copying the URL of the photo’s page from your browser’s address bar and pasting that on it’s own line, unlinked in your blog post. For more info here’s WordPress.com’s Support document on using flickr. Just be aware that if you are using the new Beta version of flickr, you may not be able to blog your photos directly from flickr to your WordPress.com site. In my photostream, that link is no longer active to me, although it was set up and working correctly in the previous version of flickr.
Update: 20 December – It seems that either from the flickr or WPcom end things have changed. Yesterday the above oembed image was just an image. Today if you mouseover the image, the flickr watermark and my name show up, along with the ability to browse the other images in my flickr photostream directly from this image. I’m going to be doing some more experimenting in the coming days.
Update 2: 20 December - We can’t get our pants on fast enough with the changes going on. For me the above image is back to what it was yesterday, i.e. a simple image with no watermark or arrows on mouseover. If you are seeing it differently, please let me know in the comments.