If you are using FileMaker 13, then the first part of you question's answer is "yes" as you can use the IsEmpty function with this property in the Inspector in order to control whether or not the button is visible.
The Insert Picture step can be set up to open a dialog where the user can then locate and select a picture file to insert into the container field. This script step is the equivalent of Insert Picture in the Insert menu or right clicking the field and selecting Insert Picture from the contextual menu that appears.
Thanks for that information
Does it only allow the functionality to insert an image path, when clicked with no paths defined nothing happens?
Never mind, fixed it - I needed to set the script to "Set Field First"
There's a check box that limits the insert to "store a reference" only as part of the script step.
You might also use the Insert File script step to insert the picture via that method as the insert file script step has more options for how the dialog looks and functions. After the script inserts the file as a file, it can use the file path in the container field to re-insert the file as a picture.