Select already existing images on server

Hello guys,

I would like some help…
I’m trying to build an eshop and in the products section I need the administrator to be able to
a) insert/upload new images for each product
OR
b) select images that already exist on server (have been uploaded in the past).
Of course this method will be used and when a product is edited/updated.

So, there will be a dropzone component handling multiple images upload and a button “Select existing Image/s” that will give the ability to browse a server’s specific path (e.g.“assets/images/products”), select one or more images and update the database field/s with the name of the image/s.
I suppose you understand what I’m trying to do and there are more cases that I will need to use this technique/method (e.g. “Featured products”).
The “upload new images” method is known but the alternative method “select already existing images” is what I am trying to find out.

Any advise or ideas will be much appreciated!
Handler: PHP
Database: MySQL