I think I get what you're saying now. You have a design with one image position that will be changed out with 100 different images. Right?
In that case you have two roads:
Use the Variables feature Horatio mentioned.
- Relink the image on your layout
- Export the artwork to your chosen format
You would get into trouble if your images aren't all the same size. It would relink them at the same size, doing whatever squishing and stretching was necessary.
A more manual alternative is ...
- Build your basic layout
- Place that file into a new document (or another artboard)
- Duplicate the artboard 100 times
- Position your images
- Run a script to export all your artboards
Set up your template design and follow these guidelines for data merge. You'll just have to tag the image element in your layout and put the path to your images into a spreadsheet so data merge can do it's thing.