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The low end Macbooks and Imacs on the current line can handle graphic work without a problem. The majority graphics, and video professionals will have no need for the extras you find in the pro line specs. Will you be doing extreme layering of images, or 3D rendering? Then you might want to look at specs, and the ability to add pci cards.... otherwise, you're safe with anything but a mini (and even then you can do a lot with one of those too!).
 
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