They’re not showing because you used the URLs of attachment pages instead of the image URLs. You go to Media > Library, click on the image thumbnail and copy the File URL: that’s the URL you must use in the widget.
Note: your images are huge; some browser versions don’t understand if an image is downsized by the theme and may display the image in its original size or distorted. You need to use an image editing application or an online tool to downsize copies of your images to the right width for your sidebar (300px), upload these copies via Media > Add New, copy the file URLs and use those URLs.
Alternative: use Text widgets instead, with the coding I’m showing here: http://wpbtips.wordpress.com/2009/04/01/codes-useful-for-text-widgets/