[David Lame]

GRIP is your friend.

Set up grip with your camera as the source, and your LED ring running. Add an HSV color filter, and display the output of those things. Adjust the sliders until you have all of what you want, and none of what you don't.

Well, you might not get to "all" and "none", depending on illumination, background, etc, but you should be able to get to a point where you have a big blob where that tape is, and a few patches of miscellaneous other spots that are not as big as the tape.

ETA: If you can't use your camera as a GRIP source for some reason (like in my case the camera is attached to a Rasp Pi), capture some still photos and import them into GRIP. And there are other ways to do this. I just use GRIP because it is very good, very free, and shared by the FIRST community so there will be lots of advice if you can't get it working.