Hi - not sure that I completely understand your need - sorry? Do you want to add a 'caption' to the image and then print out w/ the image + caption? If so, then not sure that is possible in Preview, but fairly new to OS X, so will await responses from others.
Now, if you have Keynote, then you can easily insert an image and then make a text box to show a caption - example below from my MBPro - let us know if this is what you want or if you have another idea in mind - Dave
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