The image with the lowest compression of 1.

If you had a slow connection, you would notice that at first the image would be blocky and unclear.  As the image keeps loading, the image will become clearer.

The image with a compression of 15.  Notice that the file size has been significantly reduced and the image quality is still very good.

The image with a compression of 30.  Notice that the file size has been reduced further and the image quality is still very good.

The image with a compression of 60.  Notice that the file size has been reduced further. However the image is starting to loose detail and artifacts are appearing in some areas.

The image with a compression of 90.  Although the file size is very small, the image quality is very poor.

This example shows what happens if the GIF format is used instead of the JPEG format on a photographic quality image.  Notice how the blue hues in the sky look blotchy.  This is due to the 256 color limitation with a GIF.  The GIF format is not recommended photographic quality images.