Guenter,
Thank you for your interest in mosaic dataset.
Yes, to be able to show which image currently she/he is identifying is a very useful feature. We are working on a better way to present this to the users. currently, what you can do is to open the mosaic layer property page, choose Selection-> Select Visible Raster, the selected raster will be highlighted in the display, and you can see the information of the selected raster if you open attribute table. Click on the raster cell in the raster field, you will see the preview, source information, and the metadata of that raster.
Thank your for the feedback.
Hong Xu,
Team Raster