Printing these forms can be more expensive than the usual generic forms, and they are substantially less fexible in terms of data types that may be contained and interpreted from the form. One example is the ability to perform mark recognition on faxed forms which was introduced by Cardiff Software with their Teleform product. Another example is the use imaging systems to process warranty or circulation control cards in conjunction with OCR and ICR recognition for the text. Image based technologies are more forgiving to variations in color, location and quality of marks are thus allow standard black and white laser printed forms or general purpose forms to be accurately converted. Conceptually locating and converting a mark from a scanned image is simple.
Scanned images create bitmaps which are simple arrays of black and white dots.
If a page is perfectly scanned with no skew or shift, and if the marks are carefully completed it's simple to know the exact expected location of every point or group of points on a page, such as a 40X40 pixel square representing the place to expect a mark. The presence or absence of the mark is decided simply by looking at the ratio of black pixels over the total number of pixels in the area. When the calculated value reaches a certain threshold, there's a mark. All scanners and faxes generate skewed and shifted images. In addition, people often fill in forms quickly not paying attention to the exact location of their marks, not completely filling in the box and using light pencils.