App developed for product customization

Hi, I have a website build on shopify and have mobile accessory as my product line. I need to develop an app which will add product customization for my products. I have 20 products which are basically mobile covers. I want some customizations for them like name or image insertion with positioning before going to cart. see liks for example: [login to view URL] [login to view URL] please bid if you have worked on shopify development.