I take it because you want to delete them, you do not want to keep them, that is, transfer them off the iPad to a PC/Mac, NAS for storage. I find that in the process of taking them off, I can also delete them in a bulk fashion, thus removing from the iPad, and having them stored for future use.
I plug my iPad into my PC and wait for the windows dialog to come up. I select the option to view folder and navigate down to the folders within the DCIM folder. The photos will be here. I drag and drop required photos to their destination. Once transferred, I highlight the photos and delete.
When I go back to camera roll, the deleted photos are now gone. There are other ways to delete the photos on the iPad of course, but this is the method I use in conjunction with moving to storage.
