I don't have sufficient need to justify installing an OCR program but I do occasionally need to convert an image containing text into real text. Luckily I stumbled on a nifty web service that does the job for free.
It's called http://www.free-ocr.com/ and it will accept images up to 2MB in PDF, JPG, GIF, TIFF or BMP formats
I tried it on screen shots of a web site and screen shots of a PDF document and it worked perfectly.
Some screen capture programs have OCR built in but most don't. If yours doesn't you should bookmark this site as one day you will need it.