To my knowledge, one of the few ways to insert graphics into a Duxbury files consists of using Duxbury's free QuickTac program. The latest version is 4.1 and information about it can be found under the Products section on Duxbury's website. I have not used this program for any graphics I have produced and honestly haven't even explored its features that much.
I typically use CorelDRAW for all of my graphics, paste the braille into the graphics file and send two separate files to the customer.
In the future, with the eBraille initiative, the idea is to combine the graphics file and braille file into one eBraille file to avoid sending so many separate elements to the customer/reader. More information can be found about the status of that project in this NBA webinar from June: https://www.nationalbraille.org/resources/webinars/2024-ebraille-update/.