By using this feature, you can let your customers upload their own background image.
Customer-uploaded background images are not displayed as the product images; they are only displayed on the visualiser and review screens.
Please follow these instructions to allow customsers to upload background Images to your customiser:
In the admin, click on "Customisers"
Click on the Customiser which you want to edit
On the right-hand side menu, click on "Background Images"
Ensure Enable Preview Images is already selected.
Ensure that Allow customers to upload background images is selected
At the bottom of the form please click Save.