Thanks for your comments. Another reason for not using "img.setHeight()" is that this method does not keep the image's aspect ratio. Below two pictures show the difference between "img.setHeight()" and using selectors.
![image](https://f.cloud.github.com/assets/4326886/1927743/a550070c-7e66-11e3-9569-4c42f0fe4bef.png)
The above uses setting the Height and width to 480px.
![image](https://f.cloud.github.com/assets/4326886/1927751/e0aa73dc-7e66-11e3-92d3-e7b1ee775dd0.png)
The above uses selectors.

Actually in my previous project, we used a different selector rather than "img", and binding the servlet with the parbase resourcetype as similar as Justin mentioned. Because when no "XXX.YYY" selector appeared in request URI, the servlet also works, i think it does not make a difference when using "size-img" or just "img". 

But AnyWay, as David mentioned before,  my component should be "hard-pressed to DOS against CPU/Mem" And Also it is duplicated with Named Transform Image Servlet. So I plan to just to close the pull request.