I have a client who wants to build a Shopify store on which the customer can personalize the drawings she creates in the same way as in https://gossby.com/5E4F849E84366MD/Personalized_Mug_-_Couple_and_Dog._Life_Is_Better_With_A_Dog.
Are these guys using a Shopify app or is it something that was developed exclusively for Gossby.com?
Thanks for your help!
This doesn't look to be a Shopify Store so their options are most likely created custom for their store.
But this can be recreated with a Product Options app, we offer one that would be able to do this:
You can see the app working on the following example store: