DOCBOOK-APPS: jpeg graphics in RTF and HTML outputs: What am I doingwrong?

[Thomas Colby <t dot colby at science-factory dot com>]

      I'm new to DocBook and to mark-up languages in general, but I'm
trying, nonetheless, to compose some documentation for both print and
browser-based publications.  Most parts of the process have gone
swimmingly, but the graphics are a sticky wicket.
     Using the default stylesheets, I find that TIFF files look good in
my RTF documents, but present problems in HTML versions on my browser
(they do not appear integrated into the documents).  JPEG files look
beautiful in the HTML form, but appear with a distorted aspect ratio in
RTF outputs, they've become "taller"-as if seen in a funhouse mirror
(their width doesn't vary).
     The TIFF and JPEG versions of the same graphic look the same when
opened in the GIMP or other apps.  Where does this elongation come from?
Where should I begin to look for the problem?  Is there an attribute I'm
not setting?  I would like to use JPEG's for everything, if possible.
Should I resign myself to having two sets of graphic files?
     I tried using mediaobjects to provide alternate forms, only to find
that in this context, I couldn't get TIFF files to work anymore.
Here are the cases:

This formulation works fine for RTF files but creates problems when
creating an HTML output:
    <informalfigure>
    <graphic  fileref="graphics/tiffs/picture1.tif"></graphic>
    </informalfigure>

This results in "tall" figures in RTF files, normal ones in HTML:
    <informalfigure>
    <graphic  fileref="graphics/jpegs/picture1.jpg"></graphic>
    </informalfigure>

This results in "tall" figures in RTF, too.
    <informalfigure>
    <mediaobject>
    <imageobject>
    <imagedata fileref="graphics/tiffs/picture1.tif" format="tiff">
    </imageobject>
    <imageobject>
    <imagedata fileref="graphics/jpegs/picture1.jpg" format="jpeg">
    </imageobject>
    </mediaobject>
    </informalfigure>

This results in no figure at all in RTF
    <informalfigure>
    <mediaobject>
    <imageobject>
    <imagedata fileref="graphics/tiffs/picture1.tif" format="tiff">
    </imageobject>
    </mediaobject>
    </informalfigure>


I'm stymied,
I blame myself,
Any advice?

Tom