Why is it that when I insert a JPEG onto a page some are grainy and others are not?

[Sarah Inchley]

I am adding JPEG photos onto a page for our company biographies and when the page is viewed, some of the photos show up grainy and others look fine.  When previewed the photo is fine.

All the photos have been resized to fit on the page using the pre-defined options on the image menu bar and this is why I don't understand why some are fine and others are not.

Has anyone come across this before?

[Bill Bailey]

What pixel width are the images set to? In the past, I have seen that when images are sized to something like 250 pixels or less, the will appear blurry.