Image Pop-Ups in PDF

Q: Is it possible to create the following behavior: PDF file has small
images on it. When the mouse moves over (or maybe the user clicks on)
the small image it brings up another image in a new window?

in PDF. You could embed JavaScript in PDF via PDFNet SDF/Cos API.
Unfortunately we don't have a specific tutorial on how to implement
this behavior. As a starting point, you may want to take a look at
Acrobat JS Guide.
A: It is possible to implement this behavior using embedded JavaScript

Thanks. Looking at that manual gave me some good ideas on what to do.
What SDF/Cos command(s) are used to add the JavaScript to a given
object? Thanks.

You would be using standard SDF/Cos API such as
dict_obj.PutString("JS", "alert('Hello World!')"). For a concrete
example, you may want to search PDFNet KB for keywords such as
"JavaScript", "JS", etc.