What is about "Manage my images"?
You can upload all images you will need during customisation process. You will use these images to place them on your items you wish to order for example on a banner.
These images must be bigger than the place holder. When you will place an image on an item then system will make a copy of that image which will be automatically resized (ratio will be preserved). The system will place it on the banner.
You will see immediately live how your banner will look like.