I think you will find image search may work to a limited extent for very special types of products I.E Pictures,art work.e.t.c.
But my experience is that most searches are done on the normal SE's.
We do get some traffic from images but in general very little and as the guy himself says.
" I realize that the type of traffic you get from Google image search is not going to convert well, but you all like to see your page views increase "
Afraid he's wrong there I prefer seeing the sales go up.
having said that your images should be optimised with correct alt tags,as it is another string to an overcrowded bow and chance could get you one sale that makes you £10,000.
you also have in google sitemaps a facility for enhanced search of images.