The url tag doesn't embed images. That does what you said- it turns them into hyperlinks. To embed an image, you need to put the link of the image into the correct bar. So hit 'reply' on my comment. You see where you type your post? That's where text goes. Now look above it. You'll see a second, completely independent place to type. It will say in light gray text, "Share a link url, image url, or youtube video." You need to put the link there, not in the actual post body.