For security reasons, and because they want to influence you to sign up for their paid services, WordPress.com’s free Blog hosting service doesn’t allow you to embed media from random sites into Widgets or Pages.
This makes sense from a security standpoint, but it’s very frustrating to Ning.com users who want to advertise their presence in their Ning.com communities by showing their membership badges on their blogs.
There’s a way around this, though: just do a screen capture and upload an image file to your WordPress.com blog, then use the Image Widget to embed it and include our Ning.com community “My Page” URL as a link destination.
Here’s a video explaining it. As usual, my videos are best viewed in full-screen mode. If the video is blurry, just go back to the beginning and re-play it, as sometimes YouTube videos are blurry while streaming.