Until recently to sell a product implied that you have a certain stock available and each time you make a delivery you decrease that stock. Complex software was invented to keep track of stock quantities, customers, providers, etc.
Nowadays a few interesting websites makes the selling process ridiculous simple, especially due to the fact that they produce the merchandise on demand (when a customer place an order). In this way the startup costs are virtually zero.
Each time a customer order a print, the site will make an on demand print of your photo, package it and sell it to the customer. You get your money for the photo and the site gets their money everything else and everybody is happy.
T-Shirts and Gifts
You upload a digital photo and the site puts it on lots of different merchandise: t-shirts, mugs, bumper stickers, etc. Most of these sites allow sellers to create shops for exposing their creations.
If you are disparate to test their services, but you are not such a good designer, you may try outsourcing the design job using sites such as: ELance or T-Shirt Logos.
This is by far my favorite. It is a self publishing service that prints your uploaded PDF as a book in the moment a customer orders. Niche or beginner authors may find the service very useful for their career.
For Romanian speaking people there is also: http://www.edituranoua.ro