Upload proof of ID at checkout

-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7.2
-- PHP version -- : 7
-- Browser(s) name and version -- : Chrome latest
-- Error-message(debug-mod must be tuned on) -- : not displaying uploaded image

Hello Hikashop Team,

I'm amazed by every update you apply to Hikashop, it's greater and greater, thanks for the good work.

I'm struggling with a little problem currently. Just started a shop to sell knives. However, in UK, the legislation forbids selling knives to minors, so as a Seller, you have to make sure that the Person you're selling to is over 18.
In order to do that, I've used the very handy custom field "Ajax Image" in the table "User" and added it to my checkout flow.

The flow seems to work, as you cannot proceed with the order if you dont upload an image.
The upload seems to work too as the ajax progression bar reaches the end and becomes green. However when I then display the list of Customers in the backend, the field where the image should be displayed, doesnt display anything. If I go into the Customer's edit page in the backend, and try to click on the picture, it give me a "Message File not found"

Same if I go into the Customer's Control Panel in the Frontend, and display "Customer Account", there is an "empty picture" logo displayed with a sequencial number as the img alt (not even the image filename) and if I click it -> blank page.

Would there be a way to display the image during checkout flow, in the backend and in the Customer's control panel? Could the Customer have the option to delete that image from his account and upload a new one ?
Also, I found on my server where those pictures got uploaded (media>com_hikashop>upload>safe), but there is no way to identify which picture corresponds to which Customer.
Is there a way this could be done?

By the way, I also tried to lift the access restriction on the "safe" folder where the pictures get uploaded, but still same behaviour, like if the images were not available.

Could really do with a bit of help.

Many Thanks
Raphael