Hi Arnab,
The solution is bit tricky for it. I guess if you use servlet then you can easily get the image of the chart because in servlet it mainly take the static image of the chart. So if you pass the url using servlet to a BLS containing a XML loader and PDF image action block and pass that URL into the XML loader then I hope you will get the PDF image of that chart. but for this only dependency is you have to use the webpage extension as .irpt not as .html.
Hope it will help you.
Regards,
Suman