If you see a picture you don't like coming up on JBS, you can choose 'Never Show Again' from the tray menu and it'll never be shown again. However if you later want to clear that list of pictures or remove a picture, then the 'Never Shown' section of the 'More Settings' dialog is where you can do that.
You can view the current picture to make sure it's one you want to see again, remove pictures from the list one by one or click 'Clear All' to clear the list completely.
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