Scaling images in a Canvas

I want to view a jpg image in a canvas and be able to see larger and
smaller versions of the jpg image.  I have tried using the scale command
but nothing happens to the image (I am reasonably sure that this working
since a line that I have drawn does get bigger and smaller as I use the
scale command).
 
I have tried $canvas->scale(tags,..)
with tags set to "all" and "image" where "image" is what I used for
'tags' in the $canvas->createImage
 
Can image scaling be done?
 
Best regards
 
Henry Merryweather