fo:external-graphic

Hi all-

I am currently using fo:external-graphic to display an image.  It is working
successfully, as we are posting it to an Adobe PDF file, and doing a local
print.  My problem is when I go to fax the same document, my image is being
squished to 75% of its original size.

Here is my exact line of code:
<fo:block space-after.optimum="50pt"><fo:external-graphic
content-width="auto" width="auto" src="{$header}"/></fo:block>

Can anybody offer any advice?
Thanks, 
Angela