This method will not decrease download time if you are resizing a large image. This is only telling the browser to display the image at a certain size once the image is downloaded.

There is also a GD (Graphics Development) library that comes with PHP. Once turned on you can resize using GD, which does it server side before sending back HTML. Once the image is resized a temporary thumbnail is generated and sent to the client. Therefore load times are reduced when images are resized smaller.

If thats too confusing search GD Library on Google.

are you talking about