HiCreativeCakeFactory I think that you might be right regards the design on the green cake - to the right in the picture. Looks like a printed pattern on rice paper (edible printing paper) I used this image transfer technique on a Christmas cake (uploaded to CC Dec 23rd 2012) My Santa pic was scanned into PC from a Christmas Card, Images can also be sourced and printed from Photos, ClipArt, graphics etc,
You could try and source the design used on the wedding invitation.The bride may be able to help in this regard - or create your own patterns using design tools in Computer applications such as MS Word,Paint or PowerPoint in Microsoft Office. However a printer with EDIBLE print cartridges only should be used.
Any image not in file format can be scanned into a PC and printed.
Another option might be to get some family member or friend with some knowlege of graphic design to reproduce a pattern similar to that on the invitation.
Its a such a beautiful cake, and I am sure that you will make a great job of it - given the right resources.
Good luck with the project!