I do not think you can.
See a similar (maybe not identical) question on the MSDN forums:
In response to:
Now, adding a task to TFS 2010, I can use the cabinet to copy / paste from OneNote to TFS. But then the image is saved as a link to my local computer and is not saved on the TFS server.
The answer was (repeatedly stated):
As I said in my previous answer, we need to add images as an attachment to work items. Open the work item in VS, click the "Attachments" tab, then click "Add" to view the images, the images will be stored on the TFS server.
Or, do it yourself and write an application
TFS provides an API that you can use to create your own tool, and not to use their web access. See this question on how to implement this specific detail (adding attachments):
Upload a file using the TFS client APIs
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