Software for analysing graphs

S

Hi,
Was just wondering if anyone knew of any (preferably free!) software that can analyse data directly from graphs? Basically, I have a few old papers that only present their data as graphs (i.e. the results are not published as tables or anything), and I want to be able to accurately read the values used to create the graph. Someone told me there was software available that can do this, but I am struggling to find it.
Thanks
:-)

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