How do I re-plot my results against existing results? I need to compare my results with other result, so I need to re-plot the other author's results against my results. 

For example I want use this fig as a way of comparing results

so is there any way to do that or any software can do that?
There are two ways to about this. The first is to contact the authors of the paper containing th graphs and ask if they can supply the data. Otherwise you can search for digitizing software on the web. I have one (open source) that comes to mind Engauge Digitizer but that is not the only one by far.