Find black pixels off of a jpeg image of a graph

So the idea is to have a jpeg image of a graph and using matlab open it and detect the data on the graph. I know that i need to detect the axis by finding the black pixels but i am unsure how to do this. The image used is attached, so what do i need to know to find the axis??

Answer 1

[Image Analyst]

Nothing is attached. Also, never use jpg for images that need to have fine details retained, such as thin graph lines. Use PNG instead. In fact I use PNG whenever possible for everything. You might also be interested in this: http://www.mathworks.com/matlabcentral/fileexchange/36904-matlab-script-for-digitizing-a-published-graph