How do I automatically fill the Link URL for an image field?

How do I automatically fill the Link URL for an image field?

Hi

I have an image field in a form, and I want the URL link (not the source) to be automatically updated by the input into a separate URL field on the same form. How can I do this with Deluge? I can't see a way of referencing the link box as a variable except for enabling or disabling the checkbox requiring the link.

Many thanks for any help.

Martin