Hi @Vish_dhaliwal,
Thanks for replying back.
I have checked the blog for which you included link in comment. I think that the process written in the ACS blog is for old version of AEM. I am currently working with AEM 6.5.2 and there is no option for "Add Watermark to Rendition" in process step because now AEM provided new additional step called "Add Watermark" which watermarked original image and its renditions.
As you know from the question i do not want to watermark original but only rendition and it is not working with "Add Watermark" step.