Assuming all artwork is vector and not placed raster images...
- Select the image with the mask
Object > Expand Appearance if Expand Appearance is available
Object > Expand
- Click the Crop button on the Pathfinder Panel
This should trim the artwork to the boundaries of the clipping mask shape. It will leave unfilled objects in some cases, so to clean up I also generally...
- Draw and unfilled, unstroked rectangle
Select > Same > Fill & Stroke
- Hit the delete key.
Or you can deselect everything and use
Object > Path > Clean Up. Just be aware of the clean up settings. If you have other objects with masks, the Clean Up command may cause issues.
Additional based on sample image....
(Image was added after I typed the above, so I left it.)
You've got a raster image there. There's no way for Illustrator to crop a raster image. None. However, you can use the Rasterino plug in from www.astutegraphics.com to crop raster images within Illustrator.
(the astute web site seems to be very, very slow at the moment)