So you have more than nine images for a given parent record?
Add another pair of fields and make this a "filtered" horizontal portal.
In your images table, add a number field (call it Group) for this example.
Add a matching number field (this can be local or global depending on the effect you want) to your parent table.
Now add this pair of match fields to your relationship:
Parent::ID = Images::ID (your current pair of fields) AND
Parent::Group = Images::Group
Now number your image records in groups of nine. (first 9 are group 1, next 9 are group 2, etc.)
Now on your parent layout with the horizontal portal, change the value in Parent::Group to move forward or backward one group of images at a time. (I've used two buttons for this with Set Field [Parent::Group; Parent::Group + 1] and Set Field [Parent::Group; Parent::Group - 1] to do this.)
Thanks for the suggestions, will give it a try.
To answer your question, at the moment each record/object has 1 image attached. The slidesheet is for the collector to browse visually 100's of objects. People forget names...but images are easy keystones...ultimately it will be used as a link to a detail report.