If you want to quickly see which Images in your database have no Personal Indexes associated with them, you can click Add Missing from your Indexes menu:
You'll then see a list of all of your Images with no Personal Indexes, as in the example below:
You can see at the top that you currently have 80 Images with no Personal Indexes associated with them.
If you want to add a Personal Index to any Image here, simply click its corresponding Action button and select View / Add Indexes:
You can then add that Index as normal.