Is anyone able to help me with an unusual problem?

My template is embedding HTML from a remote content engine that I can't control, and I would like to change the size of an image. The only img size definition is width="450" and I would like it to display at 100%. I have been able to do this with CSS in the <head> of the template that works for most everything except Outlook, and unfortunately getting the embedded code changed is out of the question. I've tried.

Is there a way to overwrite the img HTML width by using CSS in the <head>? Thanks for any help!

My Template:
<style type="text/css">
.embeddedcontent1 img {width: 100% !important; height: auto !important;max-width: 100% !important;}
<table><tr><td class="embeddedcontent1">

Embedded HTML:
<img style="" src="" width="450" height="" alt="Auburn wins 73-60, ending Dayton’s 16-game home winning streak..." title="Photos: Dayton Flyers vs. Auburn Tigers " />