Facebook sharer.php doesn't always show image?

Question

I'm trying to have a link that on click will open a facebook share popup with customized and not scraped title, summary, link and image. The code:

    <a 
onClick="window.open('https://www.facebook.com/sharer.php?s=100&amp;
p[title]=dummyTitle&amp;
p[summary]=dummySummary&amp;
p[url]=dummyURL&amp;
p[images][0]=dummyImageURL'
,'sharer','toolbar=0,status=0,width=548,height=325');"
href="javascript: void(0)">

        <h1>Click to share this product</h1>
    </a>

I followed the guidelines here:
https://developers.facebook.com/docs/opengraph/howtos/maximizing-distribution-media-content/#images

And the image sometimes shows and someother times it won't. Apparently on changing the p[url] value or add a querystring parameter the image may most likely show. I used the debugger as suggested on similar question answer to flush cache or so but unfortunately in vain.

I can't use the open graph protocol meta information cause the the page has more than a share link and they all point to the same page (but to different locations, kinda like an anchor bookmark or a permalink).

I have searched more than a dozen questions here and on other forums and blogs an accordingly changed the image size I'm using but in vain.

Have also explored the FB.UI feed and the stream.share, one can't share on friend's wall, send a message or post to a group. And the other can't take parameters to customize the share box.
More on that:
fbdevwiki.com