The first thing you need to do is upload the picture from your computer to the internet. You can do that using your WordPress.com Media Library. After you upload it, you will need to find what is called the “File URL.” The “File URL” is displayed on the Edit Media page for each image listed in the Media Library. Once you have the File URL, you can create some html that will display the image as a link. The last example on the “Text Widget Links WordPress.com Support Page” shows the html that you need to use. You will need to replace the URLs in the example with the URLs for your image and the link you want to use.