After crawling the app store and searching via Google for the past couple of weeks I still haven't found what I'm looking for.
Of course there are several apps that offer product customization, including image uploads and product previews. So it's not that I can't find them. After reading through faq's, support pages and community post about each of these apps, I always have to conclude that they can't handle what I need.
The basic order process would look something like this.
1) Customer selects a wall art product size
2) uploads a photo
3) Customers can zoom in to fit the safety lines/bleed lines of the final product
4) Customer sees a preview of the final product.
5) Customer adds product to cart
There is actually one more thing that really bothers me. That is the look and feel of most of these apps. Most of them can't be called elegant, let alone clean, minimal and intuitive.