Add to your products thumbnails a set of image link to preview and select via click the product image option.
Transfer files from "upload" directory to your OpenCart server.
Open your Opencart site admin page.
Via the menu, access the module section (Extensions -> Modules).
Find "Image Option Preview" row and click "Install".
Initialize your "Image Option Preview" clicking on edit.
Choose an Image Option that is already in your store, if your store has not Image Option, an info message will be displayed.
Customize, if you want, "Image Option Preview" settings.
Go to your store front and check the result.
vQmod 2.5.0 or higher
100% works with default theme, customized theme could need modification. If you need support with modification for theme (or other extensions compatibility), contact the email address in the read me file.