Force image smaller with onbeforeprint

I have been at this awhile, and I haven’t been able to get onbeforeprint to make a jpg go to 384×288 from 640×480. When printing, the image takes up a third of the page which forces the text down to a 2nd and sometimes 3rd page. This is fine on screen, but that size isn’t needed when printed (just a little overkill). I just don’t have enough experience with JS to find the key(s) to get the image size down the way I want it. I have over 200 jpg’s that are used for the screen and print so I don’twant to have multiple sizes of the same pictures, it is bad enough I had to do that for the thumbnails. I don’t really need anymore. If I could even get a suggestion as to the right direction to head toward it would be a big help.

Thanks