I am using a Raspberry Pi in a museum with an information intranet site loaded. We have two Pis with the same details. From time to time we need to update the site with new exhibits/information. I create the SD cards for the Pi using disk imaging from a master that I keep at home. The problem is that each time I update the site the size of the disk image roughly doubles (started at about 2Gb, now at 15Gb). I am using Raspbian GNU/Linux 7. I have deleted the contents of the trash folder. Any ideas as to how I can reduce the size of the created images?