The pictures are the user avatars the story is assigned to. The only way I know is to ask the users to remove their avatars. Unfortunately it will then place a generic picture there.
If you're not on the cloud you may be able to add code to do what your looking for. I am on the Cloud, so I can't help you with that option.
I have multiple projects that use variations of the same base workflow. The variations depend on the requirements of the project or issue type. The variations mostly come in the form of new statuses ...
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