What are the files in the /Library/Image Capture/TWAIN Data Sources/ and can they be removed?
The MP500 and MP600 are Canon all-in-one printer/scanners.

TWAIN is a driver protocol for exchanging information with scanners.

MPXXX.ds files are Canon drivers for the scanner component of these AIO printers.  Canon documentation indicates they can be removed by opening "Library, Image Capture, and TWAIN Data Sources, and move Canon MPXXX.ds to the trash", "if the MP Navigator or the MP drivers are no longer required."

Given the age of the MP600, unless you're still actively using one of these printers, the drivers should be safe to remove.