I inspected the HTML source with Firebug; but now that you asked I checked the article in Article Manager - and is the same.

And being in the Article Editor I thought that will be relevant to insert a working picture in a non-working article - so we can spot if it's the picture or the article.
So, I did this and found that the problem it's at the article, look at the attached picture, the same image gets wrong path once and corect the second.

As you can see the pictures have all the article title as their filename. This is important for the next paragraph:

Meanwhile I observed another weird thing: There is one picture that IS WORKING but it's path NEVER gets displayed , this means that path never gets into the variable $image in the image.php file!
I marked this picture with 2 question marks in the attached image, because I wonder how can it be displayed if the path value is missing at that point??

So, it seems the path reading mechanism is affected by something in the article settings or in the article itself.

Well, we are geting closer, right?

Ahh, please disregard the last part in the last message, that one with the "weird thing".
It's not weird at all, just the image is a JPG, so the case PNG with the "echo $image;" code does not aply to it.

Best regards,
Alex.

No problem, you're welcome.

I found one last thing to bring to your attention: if there is a space in the image path it gets converted in %20 and the browser shows it, but the module display the same error (...failed to open stream: No such file or directory...)

For me this is not a problem as I should not have spaces in paths (I already asked my authors to correct couple of such mistakes), but someone may have more like this.

So, I'll use the module with the customized absolute path as I said before; other than this is a unique solution (combining "strip tags", "random order" and "article thumbnail" options).

Thank you and bets regards,
Alex.