Our file delivery features are only good for delivering a single, unchanging file to your buyers. We can't automatically deliver a unique file to each buyer after purchase, and our service wouldn't add any value to the purchasing process you describe as you'd have to basically create a brand new E-junkie product each time to fill exactly one order and then never be used again... that's just a lot of unnecessary work on your end.
You don't need a special download service like ours to deliver a unique file to a buyer anyway -- it's not something like a song track where everyone who wants the song gets the same file and might like to download from a link someone else has paid for. People who want your service will have their own images to be edited, so you can deal with them directly and give them their unique download URL or send the file to them by other means.
All you really need is a way to take payment from your buyers, that can be done via PayPal directly. Everything else is something you're going to need to handle personally so you don't need to involve a shopping cart that automates download delivery after purchase.