Ability of the app to detect answers depends on the pixels and clarity of the image (brightness and contrast). Average device equipped with 2 megapixels camera will work with "perfect" brightness and contrast ratio. Getting the "perfect" condition is rather difficult without proper lighting. Devices with 5 megapixels still need the "perfect" condition. As per JKK's template above (probably captured using phone's camera), the contrast and brightness is inadequate for good detection.
A proper scanner is needed to produce the best result. We've tested 3 megapixels document scanner with built-in LED lighting and produced a very accurate detection. Not bad for sub RM200 scanner, <3 seconds to capture an image.