src/main/java/js/http/captcha/Challenge.java
private static String getValue(File file) throws NullPointerException {
		if (file == null) {
			return null;
		}
		return file.getName().toLowerCase().replaceAll(EXTENSION_REX, "").replaceAll(NOT_LETTERS_REX, " ");
	}
private static String getValue(File file) throws NullPointerException {
		if (file == null) {
			return null;
		}
		return file.getName().toLowerCase().replaceAll(EXTENSION_REX, "").replaceAll(NOT_LETTERS_REX, " ");
	}
Challenge value associated with image file. File name is converted to lower case, extension removed and non letter
characters replaces with space, that is, non letters are considered words separators.

@param file image file, null tolerated.
@return challenge value or null if given file is null.