Hi Penilorac, and welcome to technet.
Not sure what your ten hours of filemaker training covered, but it sounds like you're not familiar with the relational database concept. http://en.wikipedia.org/wiki/Relational_database_management_system
You need a table of invoices, and a table of images/lines related to invoices. The primary key field of your invoice relates to the foreign key field in your images. When your customer enters the ordering system, it should assign them a global invoice number that can be applied to all the images/lines they add.
From what you stated is needed for your system, I'd recommend you consider hiring a developer for assistance. Preferably one that specializes in Custom Web Publishing with Filemaker. Although Webdirect is a good new feature, I don't see it as necessarily meeting your needs here. CWP will allow you to completely control and customize the front end of your application that faces the customers, while the backend order fulfillment could be managed by your employees in Filemaker.
Also, you should do some research to see if there is an off-the-shelf system that meets your needs. It might save you a lot of time and money if you can find something close, and tweak it to your business. Filemaker is a great solution, but it's not always the solution.
Honestly I had so bad experience in hiring peoples or company to create something like this in the past (with another system) that I wanted to try to do it myself. I understand the relational dabase principle and I realize this is a really big project.
The problem is that it is easy enough when you are selling items like T-shirts or anything already existing. But in our case, the product is created by the clients from several options they select and they can order seberal different products. I also tried to find something to start from but the templates / plugins often show the same options which don't work for us. I am on this since a couple of months already and checked differents options with other systems. But because of the nature of what we are selling, nothing really fit. This is why I thought about filemaker because I am pretty sure I will be able to customize it to our needs.
Thank you for your answer.
FileMaker may very well be exactly the application for you to use.
You seem wiling to put in the time and energy. That's a big part of any success.
It might be helpful to break the project into parts. For instance the Custom Web Publishing (CWP) is a pretty specialized skill set within FileMaker circles and should be kept in mind but treated and executed un to itself.
As for the order creation, I think if you look again at the templates in the general business folder, particularly "Invoices", that will get you going.
The "options" your customers choose to create a product should each be considered as inventory items. They, in turn, each have a price which in aggregate form up the product and its final price. Most developers use the term "lineitems" where as that template uses the term "Invoice data".
So using the various templates to build a skeleton system, which once tested to meet your core needs, can serve as your own new template to archive your final goal.