What you're seeing is known as a moiré effect. I don't remember the technical explanation for why it happens (Dave would know), but it always makes me wonder how experienced reporters and anchors make the mistake of wearing ties and sport coats that have a fine pattern on them that causes the effect. Fine lines that have a high level of contrast with the background cause the effect.
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Jeff
Webmaster/Guide to The Point
"And he says 'I'm goin' crazy up there at the lake...'"