When you are publishing a mosaic dataset you are getting that error? Or you are publishing an iscdef through a mosaic dataset and receiving that error?
The image server authorization is not necessary when publishing a Mosaic Dataset. However, I would consider all the permissions necessary when publishing through ArcGIS Server (source rasters, overviews & GDB). If all of the permissions are correct, but you are still getting a license error, then I would confirm you have the Image Server license and the Image Server Extension license. You need the extension to publish mosaic datasets and you need the standard Image Server license to publish iscdefs.