You can select which image shall be shown in the cart going to Fancy Product Designer -> Settings -> WooCommerce -> Cart -> and enable "Customized product thumbnail". If you already selected it and it still doesn't work please open a support ticket on our website https://support.fancyproductdesigner.com/support/home so we can have a closer look at your issue.
Could I make a comment on this.
It is not sufficient to just show a thumbnail as it should also show in the written order in the cart because if as in my case its on a tshirt its to small for the customer to see subtle differences in the design.
Say for e.g. a customer orders 2 similar shirts they cannot tell the difference between the designs by the thumbnail.
Could you add this ASAP please.
Please see attached example.
You can open a feature request in our forum so we can keep this in mind for further updates: https://support.fancyproductdesigner.com/support/discussions/forums/5000217737