Why do you not want to be running swap if you are doing "disk imaging"?

(I.e., what exactly are you referring to when you say "disk imaging"?)
You might want to copy one hard drive to another.
dd if=/dev/hda of=/dev/hdb
or
dd if=/dev/hda of=/dev/hdb1/hda.img

You can restore the image by reversing the command.
dd if=/dev/hdb1/hda.img of=/dev/hda

It wouldn't work very well with the swap on hda mounted and active.
If you are creating the image to preserve evidence of a crime, or for forensic
work, you don't want knoppix to make any changes at all to the disk.

Generally, when playing with partitions, it is better not to have any mounted on that disk.

YMMV