After publishing a mosaic dataset as a Cached Image Service from ArcMap, the Image Service cell size differs from the cell size of the source mosaic dataset.
The cell size for a Cached Image Service is determined by the Tiling Scheme used when publishing the service. Each zoom level in the Tiling Scheme has a predefined cell size. When viewing the cell size property of the Image Service through ArcMap or ArcCatalog, the size of the largest scale of the tiling scheme is listed. For example, if the ArcGIS Online/Bing Maps/Google Maps tiling scheme is used, the cell size of the largest scale may be 0.298582, which corresponds to the scale at level 19. Within each scale level, a different cell size is used. This can be seen when publishing in the Service Editor properties under the Caching tab.
Use one of the following solutions to resolve the issue: