The phrase "image size" has two meanings on the Web. First you have the height and width of the image so a picture fits on your page. Second is the image file's number of bytes. Pictures for the Web are typically compressed so they will download faster.
This tool adjusts both, creating a picture file that is optimized for use on your Web site.
To resize your digital image, click the 'Browse...' button to locate your image on your local computer. Once found, select it and click OK. Your next option is to choose what your finished image size needs to be. Height or width can be adjusted to whatever pixel size you wish. Whether you pick width or height the aspect ratio of your image will be maintained. Once this is completed, just click the 'Submit button and wait for your 'Save As' menu box to appear.