There is a work-around to enable zooming, by using Zoomify.

I use a button in the Caption to link to a page showing a Zoomified version of the picture (Zoomify breaks large files into small pieces: as you zoom in, you only download the parts you are looking at). For example:  http://www.brianwatsonphoto.co.uk/Pano/index.html#1.

For this <image>, my  config.xml file looks like this:

  <image imageURL="images/tyneglow8938.jpg"
         thumbURL="thumbs/tyneglow8938.jpg"
          linkURL="z/tyneglow8938.html"
    smallImageURL="images/small/tyneglow8938.jpg">
    <title><![CDATA[The Glow on the Tyne]]></title>
    <caption><![CDATA[7,004 x 2,774 pixels <form><button type="submit" formaction='z/tyneglow8938.html' formmethod='post'>Zoom…</button></form>]]></caption>
  </image>

This lets me display high resolution versions of my quite detailed panoramas.

The only drawback is that the button won't stay on the same line as the Caption: it appears on the line below.

Hope this helps,

Brian

Steven,

Quite right, it does involve moving out of Juicebox, but as you agree might be a solution to the original poster.

Thanks for the hint about my button positioning: it works (of course), with an addition to prevent the font size in the Caption becoming larger.

Many thanks, yet again!

Brian

Steven,
The solution above works in OS X and on iPads. On my iPhone, screen touches anywhere hides Title, Caption (including my button) and Button Bar, so a touch on the button never registers on a phone.

Setting screenMode="LARGE" in config.xml seems to make no difference.

Is there a way to get my useful button to register presses on an iPhone?

Here's an example: http://www.brianwatsonphoto.co.uk/Pano/index.html#1

Thanks,

Brian

Tapping the screen on an iPhone toggles the overlay on and off by default (you can override this behavior by setting showInfoButton="TRUE") but tapping a button on the Button Bar should certainly still work. If you have a gallery where this does not work, please post a link so that I can investigate further. (I have just viewed the gallery whose link you posted and the Button Bar buttons seem to function fine on my own iOS device.) Also, check to see if you have any custom CSS which might be overriding the gallery's own CSS.

Instead of using a <form> tag, try using a regular <a> tag instead. You can then style the content of the tag using CSS.
This should hopefully work. (The <a> tag link in the first image in this demo gallery works on my iPod Touch.)