You need two relationships: one for your list of images and one for your selected image.
Let's say your image list portal refers to a table occurrence called Images and it has a serial number ID field called ImageID. We'll call your main table "parent".
Define a new field in parent, ImageSelect (you can make this a global field if you want.)
Make a second table occurrence to your Images table called SelectedImage. (Click the Images Table Occurrence box in Manage | Database | Relationships and then click the button with two overlapping plus signs.)
Drag to make a relationship: Parent::ImageSelect = SelectedImage::ImageID
Now base your second portal on SelectedImage.
Write a script and attach it to a button in the image list portal:
Set Field [Parent::ImageSelect; Images::ImageID]
That should do it.
You can add a conditional format to your Image List portal's fields to change the fill color and thus highlight them if they were the last image name to be clicked:
Images::ImageID = Parent::ImageSelect
as the condition in your conditional format.
Thank you, that did help me get the idea of what I wanted to do.
I followed you directions and it worked perfectly! thank you!