mmm, I dont think Canon Powershot A640 is the best for OCR
here is a comparison of Canon Powershot A640 with Sony N2 (canon at right, sony at left):
in my opinion, canon looks blury and less sharp than Sony's, but with good color reproduction (black is greyish, but it doesnt have purple in it as Sony's and white seems better that Sony's), however I dont know which is better for OCRing and which is more easily corrected with postprocessing, accurate colors or sharpness