A VHS videotape or DVD (no laserdisc or video CD players implement it) or digital cable/satellite boxes receiving a data stream encoded with Macrovision will cause a VCR set to record it to fail (excluding very old models, modified VCRs, or those approved for "professional usage"). This is usually visible as a scrambled picture as if the tracking were incorrect, or the picture will fade between overly light and dark. A 6-head or 8-head VCR (most are 4-head) can minimize this fluctuation, so it is not as noticeable. A DVD recorder will simply display a message saying the source is "copy-protected," and will pause the recording."
Slashdot Mirror
"Macrovision for video
i on_for_videoMacrovision
A VHS videotape or DVD (no laserdisc or video CD players implement it) or digital cable/satellite boxes receiving a data stream encoded with Macrovision will cause a VCR set to record it to fail (excluding very old models, modified VCRs, or those approved for "professional usage"). This is usually visible as a scrambled picture as if the tracking were incorrect, or the picture will fade between overly light and dark. A 6-head or 8-head VCR (most are 4-head) can minimize this fluctuation, so it is not as noticeable. A DVD recorder will simply display a message saying the source is "copy-protected," and will pause the recording."
http://en.wikipedia.org/wiki/Macrovision#Macrovis
So there is some form of DRM on VHS too.