You can preview an
optimized image in any web browser installed on your system. The
browser preview displays the image with a caption listing the image’s
file type, pixel dimensions, file size, compression specifications,
and other HTML information.
Open the image you want to preview.
Select File > Save For Web, and apply your
optimization settings.
Choose a browser from the Preview In menu in the lower-right corner
of the optimized image, or click the browser icon to launch
your default web browser.