DITA CMS lets you compare documents with other documents, and with earlier versions of themselves.
Inevitably, you will need at some point to see what the exact differences are between two documents. You can compare topics and maps with their earlier versions or with other documents of the same type.
You can also generate a report that tells you which topics and images are shared in common by a given set of maps.
Compare is not, however, available for images or resources.