I am trying to set up a template which will display different maps based on layer definitions. One of the layers is a raster layer. Is it possible to combine a number of overlapping images into a single layer so specific images can be selected with a definition query?
Yes with a Mosaic Dataset:
A mosaic dataset allows you to store, manage, view, and query small to vast collections of raster and image data. It is a data model within the geodatabase used to manage a collection of raster datasets (images) stored as a catalog and viewed as a mosaicked image