It's called Macrovision, and most DVDs include it along with most VHS tapes. Whenever you play them *through* a VCR you'll see shifting in brightness, color, distortion, etc. There are a few devices you can get to remove the standard Macrovision on VHS tapes, but DVD has an additional version called "Colorstripe" that AFAIK can't be removed. If your projector has an S-Video input, you'd be best to use that.