See original article (Dealing with images in content management systems)...
Samples
Use the following component to upload your raw image and
create the web image. Once your raw image has been uploaded the system will
generate the canvas as a floating HTML layer on the page. The system will
scale your selection so that the finished
image is 203 pixels wide, no matter what shape your crop area was.
Now for the home page image. You can either upload a new
image or reuse one you've already uploaded by clicking the "previous images"
button. In this case, both the width and
height are constrained which means that the finished image has a fixed aspect
ratio. The selection box maintains this fixed aspect ratio as you change its
size.
Finally the thumbnail image. This too is constrained, this
time to a square shape: