Hi,
In the settings of the HikaShop cart module, in the Joomla modules manager, you have a "mini cart" option that you can se to dropdown for that.
Once that's done, you'll have a small text like "X items for Y CHF" displayed by the cart, and when you hover / click on that text you'll get a dropdown of the products in the cart with a bit more details.
That small text is displayed using a translation:
X_ITEMS_FOR_X="%s items for %s"
And there are other translations:
X_ITEM_FOR_X="%s item for %s"
TOTAL_IN_CART_X="Total : %s"
CART_EMPTY="The cart is empty"
So you can then use translation overrides to add an image:
www.hikashop.com/download/languages.html#modify
For example:
X_ITEMS_FOR_X="<img src='https://mywebsite.com/my_cart_icon.jpg' class='cart_icon'/>%s items for %s"