Interference Pattern on photos in iWeb

[pbridges]

I added two new photos to an iWeb page by dragging them from iPhoto (as I normally do).
Both photos now show a strong interference pattern (reminds me of an old TV picture using an antenna).
I attach an example of part of 1 photo.

Both photos look fine in Preview, Photoshop & iPhoto.
Can anyone suggest how to avoid this problem ?

[pbridges]

I put the same query on the iWeb Apple Discussion Group, and got some help:

Applying a Photoshop Noise Median Filter with a Radius Value = 3 to the photos worked.