Develop an iPhone / iPad app

I'm a photographer and would like to create an app that allows me to sell a set of about 20 images that can be used as a desktop image / wallpaper. I'd like the user to be able to pick one particular image to use until he decides to pick another, or to have the app cycle through the images randomly. I require your guidance in getting the app on iTunes. I also want to offer it as a digital download from my own website. I have the shopping cart function already worked out. I would like to be able to change the images contained in the app myself.