Since you don't specify an OS, here is the way I'd do it in linux.plug in the card to your card reader.Mount it (it should mount as any old sdX#)dd if=/dev/sdX# of=/path/to/save/location/image.dd sync=noerror,notrunc bs=1kThis will give you an exact copy of the first 'parition' (if its partitioned. If not don't worry about it). You can mount these with a local loopback as well to pick files off of the images.If you are worried about file size, you can alway so something like to get it to be smaller and more compact.
Cloning SD card is a way of backing up data in case of SD card corruption. The following part will show you how to clone Raspberry Pi SD card on Windows computers. You can use this method to clone SD cards with any file systems like NTFS, FAT32, exFAT, ext2, ext3 or ext4.