In Bridge is it possible to tell if an image is linked to an IndDesign file? I have many images that are licensed but not yet used.

Yes — you can do this the other way round in Bridge, using Bridge's Find dialog:

1. In Bridge, open Find.

2. In Look in, choose the folder that holds your InDesign (.indd) files.

3. Under Criteria, set All Metadata — contains — and type the image file name, e.g. File-A.psd.

4. Tick Include All Subfolders and Include Non-indexed Files, then click Find.

Bridge will list the .indd files whose metadata contains that file name — those are the documents linking to the image. If a licensed image returns no .indd files in that folder, it isn't linked there.

One tip: if the file name has spaces, use %20 in place of each space in the search, e.g. My%20Image.tif.