https://www.wix.com/support/html5/article/request-creating-a-dropdown-menu-with-images-or-icons

Raffaele,

Create a new widget for your Selection field (eg: with_image )  and add in xml.

Example

<field name="field_name" widget=""with_image"/>

Refer :https://www.odoo.com/documentation/9.0/howtos/web.html#read-write-field

It is not a simple solution

All the best  !