What causes this ?

[Rolland]

What is causing the frame of the windmill to look the way it does?....This was shot with a cannon S3 IS, & looked this way before sizing or cropping.

 

[Rolland]

I think I figured out my own answer .....It looks ok above, but below is what I was talking about, and it was caused by the viewer fitting it to screen size.....

 

[Garbz]

Lack of decent digital interpolation.

You're scaling the image down. That is using a nearest-neighbour interpolation process. It just looks at the closest pixel mathematically and assumes that colour.

What you want to do is some kind of better interpolation which any decent resizing program will allow you to select, such as bicubic or billinear which examine rows of surrounding pixels, do some math, average them, and sharpen the result.