Image caption in text widget

Hey people!

Adding an image caption in an ordinary post works okay. But how do I add an image caption in the text widget?

I have tried to put in the code that I get from an ordinary post with image and caption – using (1) the brackets [] that shows in the editor and by (2) changing them to HTML tags <>. None of these seem to work. I get the image in both cases, but without caption. With (1) I also get the brackets with the code as output. Surely there is a HTML tag solution. Or am I being overly optimistic?

/Daniel